Sefton Park, Stoke Poges

The Residential Option – Green Belt/Grey Belt

The site is washed over in planning policy terms by its designation as part of the Metropolitan Green Belt.

The entire area of the former South Bucks District is designated as Green Belt. This designation has remained largely unchanged for decades. Under Section 17 of the Planning and Compulsory Purchase Act 2004 and Paragraph 34 of the NPPF (2024), local plans, including Green Belt policies, must be reviewed at least every five years. The age and rigidity of the existing designation is therefore a material consideration in determining whether certain parcels continue to serve a strategic Green Belt function.

This also means that South Bucks needs to build on Green Belt to discharge its duties to meet the development needs of its administrative area. Accordingly, sites that can demonstrate they qualify for ‘grey belt’ classification, should be looked upon more favourably.

Definition of Grey Belt

The latest iteration of the National Planning Policy Framework (NPPF) introduced the concept of grey belt, allowing for the identification of land within the Green Belt that plays a limited strategic role and may be suitable for future consideration through plan-making, or on a case-by-case basis upon receipt of an application for development.

A site may be classified as grey belt where it performs weakly or not at all against the following Green Belt purposes (NPPF Paragraph 143):

(a) “to check the unrestricted sprawl of large built-up areas”;

(b) “to prevent neighbouring towns merging into one another”;

(d) “to preserve the setting and special character of historic towns.”

In the context of Green Belt policy, the Planning Practice Guidance provides authoritative clarification on how Green Belt purposes should be interpreted and applied, both in plan-making and on a case-by-case basis when assessing development proposals. 

A detailed analysis of the site’s characteristics according to the ‘tests’  above has been completed by Sefton Park Ltd. and the conclusion is that the entire site can be classified as grey belt

The Residential Option – Heritage

A Preliminary Heritage Statement has been prepared with respect of the Pre -Application Enquiry proposals for the northern part of the site which currently includes all the standing modern buildings of the business park. The Manor House is excluded from either of the areas.

There is one Listed Building within the area covered by the Master Plan for the northern half of the site – The Manor House, which is Grade II Listed. It was originally built as a small Georgian country house and was altered and remodelled in 1911. The park which related to the Manor is not on the Register of Historic Parks and Gardens. The entrance gates to the former southern driveway are Grade II Listed but these are not within the application site and the driveway has not served the northern part of the site since this part of the site became used for scientific medical research in the post WWII period. The park and mansion are not within a Conservation Area. There are two further Listed Buildings outside of the park area – _the Stoke Poges school Grade II Listed to the east of the site and on Bells Hill to the west of the site. Neither of these two heritage assets immediately abut the area considered in this statement.

The Manor House and the related northern area of the park have been remodelled and redeveloped twice in the C20, first when the site became a medical research centre after WWII and secondly, at the end of the century when the site was developed as an office park. The southern area had been developed into sports facilities associated with the post war medical research facilities developed by Glaxo including a golf course and tennis courts with a separate access from Bells Hill to that of the commercial units to the north.

Due consideration of the significance of the Listed Buildings both on and adjacent the Sefton Park site has been undertaken as part of the analysis of constraints to development. The main listed building will not be part of any proposals for redevelopment. Nevertheless, its setting is also an important feature to which due consideration should also be given.

The NPPF requires any harm to the significance of a designated heritage asset including from development within its setting, to provide a clear and convincing justification. The justification in this instance is one of alack of demand for the repurposing of all existing buildings, including the heritage asset that is the Manor House. There is also the fact that the site is previously developed and that the surrounding land use being residential with good proximity to local services makes residential use of this site a viable and compatible option. If a small amount of new commercial use is realised in the north west corner of the site it will relate well to the Bells Hill Centre on the opposite side of the road.

Historic England guidance accepts that the setting of a heritage asset is not fixed and may evolve over time. The setting and wider context of the Manor House has been shown to have changed considerably in the last 80 years on two past cycles of development.

Change does not necessarily equate to harm. The assessment has demonstrated that the residential redevelopment proposals offer an opportunity to mitigate the potential for harm to the setting of The Manor House. The replacement of the two office blocks to the northeast of the site offers the potential for enhancement of the setting and retention and reinforcement of the landscape setting which survives from the former parkland and gardens once associated with the house.

The level of harm to the setting of the identified heritage asset on the site can only be considered in broad terms at this stage given that a scheme is presented as a Master Plan. It is assessed that given the proposals are not immediately adjacent to the Listed Building, this will preserve the immediate setting of the building, and no harm has been identified as resulting to this.

In broad terms the redevelopment of the northern part of the site has potential to result in either no harm or a low level of less than substantial harm to the wider setting of the heritage asset. This provisional assessment may be modified at detailed stage when the details of the mitigation measures such as landscaping and the design of the dwellings are known.

The Residential Option – Surface Water Drainage and Flood Risk

The site at Sefton Park is located within Flood Zone 1 according to the latest Government Flood Maps as shown overleaf, and not at risk of flooding from local watercourses.  Land within Flood Zone 1 is accepted for residential development.  

In considering all sources of flooding, the site recognised as being a low risk from overland surface water flooding, which is assessed at a 0.1% to 1% chance of occurring across the site.

The Government information illustrates overland flooding between the existing buildings on the northern part of the site, over the existing pond and along the southern boundary.  Only during 0.1% chance will the overland surface water flow through the site from north to south.

The surface water drainage at the site currently drains south through the existing pond to the south-east corner of the site, where it leaves the site.  The foul water drainage is pumped from the site into the adoptable foul water drainage sewer located in Bells Hill.

A full site investigation has been carried out across the site to establish ground conditions and the opportunities for infiltration.  

The surface water drainage will accommodate the existing buildings and will be restricted to outfall at the current discharge rate.  

The drainage strategy is landscape led, with surface water being routed through tree pits, and detention basins which will be landscaped.  The routing of surface water through the existing pond will be retained to ensure the water level is maintained as currently.

The Foul Water will be discharged to the existing Thames Water sewer in Bells Hill, where capacity has been confirmed as available for the development.

The Residential Option – Trees

A full tree survey and arboricultural impact assessment has been undertaken in accordance with BS 5837:2012 – Trees in Relation to Design, Demolition and Construction. The assessment covered all trees within and adjacent to the Sefton Park estate, including both the northern and southern parcels.

The survey identified a well-treed site comprising individual specimens, groups, and hedges of varying quality. Category A and B trees—those of high and moderate quality—are primarily located along the boundaries and within the established parkland areas, forming an important visual framework and contributing significantly to the character of the site. Category C trees (low quality or limited life expectancy) and Category U trees (unsuitable for retention) are interspersed throughout.

The proposed development across both parcels requires the removal of a number of trees where these conflict directly with new building footprints, roads or infrastructure. In total, approximately 100 individual trees and several small groups are proposed for removal, the majority of which are of Category C or U quality. A small number of Category B trees are also affected, although their loss has been minimised through design refinement and offset by extensive new planting.

Minor pruning will be required to a limited number of retained trees to provide clearance for construction and to improve long-term form. The extent of this work is considered minor and will not adversely affect the health or visual amenity of these trees.

The layout has been designed to avoid encroachment into the Root Protection Areas (RPAs) of key retained trees. Where incursions are unavoidable, they are within acceptable tolerances under BS 5837:2012, ranging from less than 1% to a maximum of around 15% (in isolated cases), and will be managed through specialist construction techniques such as no-dig surfaces and up-and-over pathways.

A comprehensive Tree Protection Plan and Method Statement specifying protective fencing, ground protection measures and supervision arrangements to ensure the health of retained trees throughout the construction process will be submitted. Regular on-site arboricultural supervision is required at critical stages, including fencing installation, ground protection, and pruning works.

The report concludes that, subject to adherence to the recommended protection measures, the development will not cause significant harm to retained trees. The proposals also include extensive replacement planting—approximately 135 new trees across the two parcels—to provide long-term landscape enhancement and ensure a sustainable tree stock for the future.

The Residential Option – Ecology

The development of the masterplan has been informed by the outcomes of an extensive ecology assessment for the site. The final EcIA report considers numerous habitats and species within the site and sets out avoidance strategies and recommended mitigation for development activities on site.

The northern section of the Sefton Park site contains several buildings associated with Sefton Park Business Campus surrounded by hardstanding and well-maintained amenity grassland and introduced shrubs. A grassland field is located to the east of the site. Overall, the site is bounded by woodland, trees, hedgerows and fences. Collectively the habitats within the proposed development site are assessed as being of value at the Parish level.

Extensive ecology surveys have been undertaken on the site during summer and autumn 2025 including surveys for botany, reptile, bats emergence and activity and great crested newts. The results of surveys were:

• the botany survey showed that the site had limited potential to support rare and/or priority plants due to the current management, but key vegetation areas are suggested to be protected and retained in the development.
• The results of the reptile survey found no reptiles present within the site.
• The results of the bat emergence survey found that no bats were roosting in the buildings on site.
• The results of the great crested newt eDNA survey indicated that great crested newts were not present within the ponds on site, nor the ponds within 250m of the site boundary. The results of the bat activity survey are still in progress as surveys are not yet complete.

The development of the masterplan has been aided by the outcomes of these surveys, with areas and habitats of importance proposed to be retained where possible within the masterplan. The Ecological Impact Assessment (EcIA) considers the results of the protected species surveys and sets out avoidance, mitigation and compensation measures to minimise impacts of the proposed development upon protected species residing in the site.

Ecological enhancements are proposed within the EcIA, including the creation of habitat piles, stag beetle loggeries, bat and bird boxes and native planting across the site.

Biodiversity Net Gain calculations indicate that there will be an overall net loss on the site, due to the loss of habitats and trees, but off-site credits are currently being explored to achieve the minimum of 10% net gain, as required under The Environment Act 2021.

The Residential Option – Transport, Highways and Access

A transport assessment has been carried out from which is concluded that the site is considered to be ideally located for residential development for the following reasons:

• The site is well connected to the existing pedestrian network
• There are education, retail, healthcare and leisure amenities within acceptable walking distance of the site cycling distances and therefore the location of the development is considered sustainable
• There is a bus service  that runs along Bell’s Hill providing connections into Slough Chesham and Amersham
• The closest train station is in Slough which provides frequent services to key destination London and beyond.
• A review of PIC data has revealed that there are no discernible highway safety issues that would be made worse by the development

The local amenities and bus stop locations are illustrated in the main report to be submitted with the planning application(s)

Vehicle parking for the proposed development will be determined at the full application/reserve matters stage. However, at this stage the proposals as shown on the indicative Master Plan are in accordance with adopted  local parking standards of an average of two spaces per dwelling.

A junction capacity assessment has been carried out for:

• Sefton Park / Bells Hill / Rogers Lane (northern development access) Junction
• Bells Hill / Church Lane / Farthing Green Junction
• B416 / Stoke Green Junction
• Stoke Green / Wrexham Road / Church Lane Junction
• Temple wood / Stoke Common Junction

Although the full analysis and report is imminent, it has not yet been completed but it  is most likely that it will be demonstrated that the development site access is forecast to operate with significant reserve capacity, and the proposed development will lead to a net reduction in vehicle trips when compared to the full / historic occupation of the Sefton Park Campus office floor space.

The development proposals present the opportunity to improve east – west cycle connections through the site, connecting the existing residential neighbourhoods with the school, recreation area and the village centre. This is a specific objective of the Stoke Poges Neighbourhood Plan and can be delivered by these proposals.

In respect of specific highway proposals contained within any outline planning application all matters will be reserved for approval other than the access provisions for the site off Bells Hill and the internal estate road.

Detailed proposals for the provision of a vehicular access into the site which is a significant modification of the existing access off Bells Hill Road have been developed in accordance with appropriate technical requirements for the safe and practical movement of vehicles and pedestrians. Detailed, dimensioned drawings of the proposed access, visibility splays and internal estate road together with swept path analysis for service and refuse vehicles, are submitted as part of this pre app.