10 September 2026
New Planning Law Makes Changing Your Extension Design Easier
Upcoming Section 73B legislation will allow London homeowners to easily amend existing planning permissions without starting over.
The Ministry of Housing, Communities and Local Government (MHCLG) has announced that new legislation for the much-anticipated "Section 73B" route is expected to be rolled out before Christmas. Historically, if a homeowner or developer wanted to make adjustments to a planning permission that had already been granted, they were restricted by rigid rules. They either had to use a Section 73 application for "minor material amendments" or file an entirely new planning application if the local council deemed the changes too significant. The new Section 73B route fundamentally changes this landscape. It introduces a streamlined legal pathway to vary existing planning consents, provided the proposed new development is "not substantially different" from the originally approved plans. This legislative update promises to inject much-needed flexibility into the UK planning system, cutting down bureaucratic delays and making it significantly easier to adapt architectural designs after the initial consent is secured.
At London Extend, we understand that designing and building your dream home extension is an evolving journey. Often, once initial planning permission is granted, homeowners realise they want to make adjustments. Perhaps you want to slightly enlarge the footprint of your rear extension, alter the roof pitch to accommodate a better skylight, or shift the placement of your bi-fold doors after consulting with your interior designer. Previously, even seemingly modest changes could trigger a planning nightmare.
Under the old system, local planning authorities in London were notoriously strict. If your desired modifications fell outside the narrow definition of a "minor material amendment," you were forced to submit a completely fresh planning application. This meant paying new application fees, enduring another lengthy eight-week waiting period, and risking a potential refusal from a new planning officer who might view the entire project differently.
The introduction of the Section 73B route is a game-changer for London homeowners. By allowing amendments that are "not substantially different" from the original consent, the government is providing a much wider safety net for your project's evolution. This means that if material availability changes, if your budget fluctuates and requires a design tweak, or if you simply change your mind about specific architectural details, you will no longer be held hostage by an inflexible planning system.
For our clients at London Extend, this upcoming legislation translates directly into saved time, reduced stress, and lower administrative costs. It empowers our architectural team to refine and perfect your extension's design closer to the build date. We will be able to submit a Section 73B application to your local London borough council, secure in the knowledge that the planning officers are only evaluating the specific variations, rather than putting the entire previously approved scheme back under the microscope.
As we await the final rollout of this legislation before Christmas, the team at London Extend is already preparing to integrate this streamlined process into our development management framework. If you are currently holding planning permission but have been hesitant to pursue design improvements due to red tape, this new law provides the perfect opportunity. We are here to help you leverage these UK planning law changes to ensure your final home extension perfectly matches your vision.