What is a lawful development certificate, and when do you need one?

What the London numbers show

These are government figures for all 33 London boroughs, not estimates. They are the same numbers we publish on each borough page, summed — so if a borough page and this page ever disagreed, one of them would be wrong.

The two kinds, and why the difference matters

A section 192 certificate covers proposed works and answers the question "if I build this, will it be lawful?" A section 191 certificate covers works already built and answers "is what I have already got lawful now?" They are decided on completely different evidence.

For a proposed certificate the evidence is the drawings: accurate existing and proposed plans, sections and elevations, dimensioned so the officer can measure compliance against each limit. For an existing certificate the evidence is proof of time — dated photographs, invoices, council tax or utility records, statutory declarations — because the case turns on when the works were completed rather than on what they look like.

Is it worth applying if the work is obviously permitted development?

Yes, and the reason is commercial rather than legal. Permitted development is a status with no paper trail. When you sell, the buyer's solicitor asks for evidence that the extension was lawful, and "it was permitted development" is an assertion, not evidence. The usual remedies at that point — indemnity insurance, a price reduction, a retrospective application under time pressure — all cost more than the certificate would have.

The certificate is also the cheaper failure mode. It is determined on facts, so a compliant scheme is granted; if the council disagrees, you find out before you build rather than after.

How long does it take?

The statutory period is eight weeks from validation, the same as a householder planning application, though a straightforward certificate is often decided sooner because there is no consultation stage — neighbours are not consulted on a certificate, because the council is determining a legal question rather than weighing amenity.

Validation is where the time actually goes. A certificate refused for inadequate drawings has to be reapplied for, so scale, dimensions and the existing-versus-proposed comparison need to be right the first time.

Where lawful development certificate affects the drawings

Sources

• Lawful development certificates — Planning Practice Guidance
• Town and Country Planning Act 1990, sections 191–192