A call to your local planning office will tell you what is permitted development and what will need planning permission. Needing permission does not exclude the possibility that it can be done - but I suspect that what you are considering won't need planning.

But you will need the freeholders permission- go to them when you have an idea of what you are likely to do.

Thank you Jonathan! Im trying not to get too excited & carried away with plans until i know i can extend the 1st floor as well as ground!

Hi Sarah

I would advise that an extension to a flat needs planning permission in addition to getting Freeholders consent. The Planning portal states that: "To add an extension to your flat you must apply for planning permission."

Wandsworth Council does have a duty planner service however if you feel the advice is not clear and they only point you to policy documents they do also have a paid for pre-application service which is £135 for a householder. You need to submit proper drawings for the pre-app as if you were for planning to get the best out of this service.

Freeholder's consent usually requires planning permission & building control approval to be obtained and then submitted to the Freeholder but it wouldn't hurt to get the Freeholder's agreement in principal to an extension before embarking on planning. if you haven't already.

I hope this helps, good luck with your project.
Marienne