Borough design guides and supplementary planning documents explain how adopted policies are applied, but an SPD is not itself part of the statutory development plan. A new-style supplementary plan has a different legal status. Check which type of document you are reading before treating its advice as an adopted development-plan policy. [1][2]
What an SPD can do
National planning guidance explains that SPDs add detail to adopted policies and are material considerations in decisions. They should not introduce new planning policies. They can help explain matters such as design, but their role is to support the plan rather than replace it. [1]
For an extension or roof alteration, read the policy, the guide's explanatory text and the relevant illustration together. A diagram illustrating an acceptable response in one building type is not a reason to ignore the document's scope or the property's different circumstances. Treating the illustration as a standalone permission would confuse guidance with the decision-making framework. [1][2]
The important 2026 change
England's new plan-making system came into force on 25 March 2026. It includes a process for supplementary plans, with their own preparation and examination requirements. The amended development-plan legislation recognises adopted supplementary plans as part of the statutory development plan. They are not simply SPDs with a shorter title. [3][4][2]
The transitional regulations allowed councils to continue preparing SPDs only where they were adopted no later than 30 June 2026. Existing SPDs did not all disappear on 1 July. They continue under the saving provisions until revoked or until the development-plan document containing the policy they explain ceases to have effect under the relevant transition provisions. [5]
This makes both the guide's date and the status of its underlying plan important. A recently updated download page does not, by itself, demonstrate that an old SPD has been newly adopted or remains applicable in every respect. [5]
A current borough example
Bexley adopted Design Guide Part 2 on 29 June 2026. Its published material separates guidance on building alterations and extensions, small sites, area types and a technical handbook. That structure illustrates why a reader should identify both the project type and the relevant local context rather than stopping at a single general design page. [6]
The Bexley adoption date also sits immediately before the statutory SPD deadline. The existence of an SPD adopted then is not evidence that councils can continue adopting new SPDs indefinitely under the old procedure. [6][5]
Check for withdrawn or superseded advice
London-wide guidance can change independently of a borough's design document. The March 2026 housing package withdrew specific dual-aspect and homes-per-core guidance benchmarks while retaining London Plan Policy D6. A quotation from an earlier design assessment may therefore describe advice that is no longer current. [7]
For a live project, note whether the document is an adopted SPD, older supplementary planning guidance, an adopted supplementary plan or a draft. Also identify any formal revocation, replacement or withdrawal affecting the provision being relied on. The legal distinctions determine how the material should be used. [1][2][5]
A useful reading sequence
- Identify the operative plan policy and the property's relevant designation or area.
- Read the current guide that explains that policy, including qualifications around its diagrams.
- Check the guide's adoption and replacement information, and whether the parent policy remains operative.
- Keep draft guidance separate and record the policy basis for any proposed departure.
This sequence is a practical document-checking method, not a new validation requirement. It follows the distinction between development-plan policy, supporting material and emerging proposals. [1][2][8]