Hi,
We currently have had our planning application approved by Lambeth and building works have begun. they are really busy at the moment but I have to say we have had a good planning officer who gave us suggestions of how to change the drawing in order to get the planning approved.
1. If you just want a side return extension and go for a 6 x 6 m you can apply for permitted development side return infill extension. These are very easy to obtain
2. Anything bigger then full planning application BUT our suggestion for a wrap around, was just to go in by 1 brick size right at the end of where the bi-fold doors end, so therefore this falls into the planning "rules". We were advised by our planning officer to do this. so creating the L shape they looking for but barely!
God i hope this makes sense as am not explaining myself too well here!!
Lambeth apparently is not as easy as Wandsworth but my experience with calling planning and speaking to people have helped us have a successful full planning application approved. I have therefore had a very positive exp.
good luck and shout if you have any other questions!