Retrospective Planning Permission: How to Regularise Unlawful Development

Introduction

Retrospective planning applications — applications for planning permission for works that have already been carried out — are more common than many homeowners realise. They arise when development has been carried out without permission (whether by oversight, misunderstanding, or deliberate choice), or when works carried out under permitted development turn out to require planning permission. This guide explains how retrospective planning applications work, how they are assessed, and what happens when they are refused. For related guidance, see our enforcement notice guide, LDC guide and Camden planning guide.

Can You Apply Retrospectively?

Yes. Section 73A of the Town and Country Planning Act 1990 explicitly provides for retrospective planning applications — applications for permission for development that has already been carried out. There is no penalty in planning law for applying retrospectively (though enforcement consequences remain possible if the application is refused). The planning authority must assess a retrospective application on its planning merits, exactly as it would assess a prospective application. The fact that the works have already been built does not help or hinder the application in principle — the decision must be made on planning grounds.

In practice, the main difference is:

• You have less flexibility to amend the scheme in response to planning officer feedback, because the works are already built. Changes would require physical demolition or alteration.
• If the application is refused, the planning authority can take enforcement action to require the works to be removed or remedied.

Why Do Retrospective Applications Arise?

Common reasons for retrospective applications in NW3:

• The homeowner or builder incorrectly believed works were permitted development — a common situation in conservation areas where Article 4 directions remove many PD rights
• A builder started works before planning permission was obtained (sometimes without the homeowner's knowledge)
• Works deviated from the approved plans during construction — perhaps a window was enlarged or relocated, an extension grew slightly beyond the approved dimensions
• A completed extension was not signed off against building regulations, and when selling the property the planning status of the extension must be regularised

How Camden and Barnet Assess Retrospective Applications

Camden and Barnet assess retrospective applications using the same policies and criteria as prospective applications. The planning merits of the works as built are evaluated against:

• The development plan (Camden or Barnet Local Plan policies)
• Conservation area character and appearance (for NW3 properties)
• Impact on neighbours' amenity
• Design quality of the completed works
• Any material considerations

Camden's planning officers do not have a formal policy of refusing retrospective applications on principle, but they may take a less flexible approach than on a prospective application — there is less scope for negotiating design amendments to address concerns when the works are already built.

If a Retrospective Application Is Refused

If Camden refuses a retrospective application, the planning authority can proceed with enforcement action. Options for the homeowner then are:

• Planning appeal: Appeal the refusal to the Planning Inspectorate. The same appeal rights apply as to any planning refusal. See our planning appeal guide.
• Enforcement appeal: If an enforcement notice has been issued, appeal the notice to the Planning Inspectorate — often combined with a planning appeal.
• Comply with the enforcement notice: Remove, alter or restore the development in accordance with the notice.
• Negotiate a modified scheme: In some cases, modifying the built works (reducing the extension, changing the materials, altering the window configuration) can address planning objections and make a revised retrospective application acceptable.

Retrospective vs Proactive: The Risk Comparison

Planning practitioners consistently advise that applying for planning permission before carrying out works is significantly less risky than relying on retrospective application. The reasons:

• A prospective application can be refined in response to planning officer feedback before works start — at low cost (amended drawings)
• A retrospective refusal may require expensive physical changes or demolition
• Enforcement notices carry criminal penalties for non-compliance
• Retrospective matters create disclosure obligations at the point of property sale — buyers and their solicitors will identify enforcement notices and retrospective permissions on the planning register

The cost of a planning application (architect's fees, application fee, a few months' time) is almost always far less than the cost of enforcement, demolition or legal dispute.

Conclusion

Retrospective planning permission is a legitimate and frequently used route to regularise unlawful development in NW3. The assessment criteria are the same as for prospective applications — good design, appropriate materials, and minimal impact on neighbours and the conservation area remain the keys to a successful application. But the risks of retrospective application — reduced flexibility, potential enforcement action, and disclosure obligations — reinforce the importance of getting planning right the first time. Use our free matching service to find an architect who manages the planning process proactively and identifies requirements before works begin. For cost guidance, visit hampsteadrenovationcosts.co.uk.