Lawful Development Certificate vs Planning Permission: Which Do You Need?

If you're planning a home extension in London, you'll almost certainly come across both terms: planning permission and a Lawful Development Certificate (also called a Certificate of Lawfulness). They sound similar. They're not. Understanding the difference will save you time, money, and a significant amount of confusion.

The Core Difference in One Sentence

Planning permission is the council's approval for development that requires their consent. A Lawful Development Certificate is the council's confirmation that your development doesn't require their consent — because it falls within your existing legal rights. One is permission. The other is confirmation.

What Is Planning Permission?

How it works

When you apply for planning permission, you're asking your local planning authority to approve proposed development that falls outside your automatic permitted development rights. The council assesses your application against its planning policies — covering design, impact on neighbours, relationship to the street scene, and dozens of other factors. They exercise discretion: they can approve, refuse, or approve with conditions. Neighbours and third parties can comment on the application, and those comments are considered in the decision.

When you need it for a home extension in London

You need planning permission for any extension that exceeds your permitted development rights. For a London terraced or semi-detached house, this typically means: a rear extension deeper than 6 metres (or 8 metres for detached), any double storey extension that doesn't meet the strict PD rules, any side extension, any extension in a conservation area where PD is removed, and any extension on a listed building.

What Is a Lawful Development Certificate?

Proposed LDC

A Proposed Lawful Development Certificate (PLDC) confirms that your planned works, if carried out as described, will be lawful without planning permission. You apply before building. The council assesses the application based purely on whether the works meet the permitted development rules — not on whether they're good design or acceptable policy. There's no discretion: if the rules are met, the certificate must be granted.

Existing LDC

An Existing Lawful Development Certificate (ELDC) confirms that works already carried out are lawful — either because they fell within permitted development, or because the enforcement time limit (now 10 years) has expired. Used when you need to demonstrate legal compliance to a buyer or mortgage lender, or to defend against enforcement action.

Side-by-Side Comparison

Purpose

Planning permission: authorises development that requires approval. LDC: confirms that development is lawful without approval.

Decision-making process

Planning permission: the council exercises discretion, weighing up planning merits against policies. Neighbours can object. An LDC: the council makes a legal determination. There's no discretion — if you meet the rules, you get the certificate. Neighbours cannot object to an LDC application.

Cost

Planning permission (householder application): £548 from April 2026 in England. LDC: £258 for a proposed or existing LDC for a householder development. Both require professional fees on top for architectural drawings and application preparation.

Timeline

Planning permission: 8 weeks statutory, often 10–13 weeks in practice in London. LDC: 8 weeks statutory, generally met. In both cases, the clock starts from validation of the application, not submission.

Risk of refusal

Planning permission: significant — the council is making a policy judgement, and local objections, conservation area status, or design concerns can result in refusal. LDC: low if the application is well-prepared and the works genuinely fall within PD rights. The council is making a legal determination, not a policy judgement.

Legal status

Planning permission creates a right to develop that runs with the land. An LDC recognises an existing legal right — it doesn't create a new one. Both are permanent legal documents and both should be retained for future property transactions.

When to Choose an LDC Over Planning Permission

Scenario 1: Single storey rear extension within permitted development limits

If your planned rear extension extends no more than 3 metres (terraced/semi-detached) or 4 metres (detached) beyond the original rear wall, is single storey, and your home is not in a conservation area or subject to an Article 4 Direction, your extension is almost certainly permitted development. Apply for a Proposed LDC rather than planning permission — it's quicker, cheaper, and the outcome is more certain.

Scenario 2: Loft conversion under permitted development

A rear dormer or rooflight loft conversion that stays within the permitted volume limits (40 cubic metres for terraced, 50 for others) and doesn't raise the ridge height should be permitted development on a standard house. A Proposed LDC confirms this before you spend money on construction.

Scenario 3: Regularising old works before a property sale

If you're selling a property with an extension or conversion built without planning permission, an Existing LDC is often the right solution — provided the works were completed more than 10 years ago and you can evidence this. It's usually quicker and more straightforward than trying to get retrospective planning permission.

When Planning Permission Is the Only Option

You need planning permission (not an LDC) in the following situations:

• Any extension that exceeds the permitted development size limits

• Any extension in a conservation area where PD rights are removed

• Any side extension (always requires permission in conservation areas)

• Any double storey extension (unless it meets the strict PD rules, which most don't)

• Works to a listed building

• New buildings or structures in the garden beyond the PD allowances

Common Misconceptions

'I don't need anything — it's permitted development.' You're probably right, but without an LDC you have no formal evidence. Future buyers' solicitors will ask for documentation. 'An LDC means I've got planning permission.' No — an LDC confirms you don't need it. They're different documents. 'I can object to my neighbour's LDC application.' You can comment, but your comments about planning merits cannot be taken into account — only the legal question of whether the works are lawful is relevant.

Can You Have Both?

Yes — and it sometimes makes sense. If you build under permitted development without an LDC and later want formal confirmation, you can apply for an Existing LDC (provided it was completed lawfully). You can also have both planning permission for works that required it and an LDC for associated permitted development works. The two documents cover different things and are not mutually exclusive.

Which Route Is Right for Your London Extension?

The answer depends on what you're building and where. If your extension comfortably fits within the permitted development rules and your home isn't in a conservation area, an LDC is almost always the right choice — it's quicker, cheaper, and carries less risk. If you're building something larger, in a conservation area, or on a double storey, you need planning permission. In borderline cases — where you're not certain whether permitted development applies — a Proposed LDC is an efficient way to get clarity before committing to construction.

Frequently Asked Questions

Is an LDC cheaper than planning permission?

The application fee is lower (£258 vs £548), but the professional fees are similar. In both cases you'll need architectural drawings and a planning statement. The real advantage of the LDC route is speed and certainty, not cost.

How long does an LDC take?

8 weeks statutory from validation of the application — the same as a planning application. In practice, LDC applications tend to be determined within the statutory period more reliably than planning applications.

Can my neighbours block my LDC?

No. Neighbours are notified of LDC applications and can submit comments, but those comments cannot be considered in the decision. The council is making a purely legal determination — not a policy judgement. Neighbour objections are irrelevant to the outcome.

Not sure which route applies to your project? Book a free architectural advice call with Studio : MASS. We'll confirm your permitted development position and recommend the right approach from the start.