From what I see and hear, these extensions (side return and loft) are becoming more and more common in this area, as people find moving to a bigger house is too expensive. The house opposite mine is having exactly this done at the moment.

It might be worth you having a look at other planning applications in the area, you'll be able to see details of the companies that have done them. and plans submitted, many of the houses in this area are of a similar design so this should be useful. You can search for planning applications here:

http://www.planningfinder.co.uk/

I'll PM you the link to the planning application for the house on my road.

Good luck! I'd love to do this if we could afford it!