Hi:the plans submitted to the Council indicate that the outer wall which affects us will be a double brick layer. The garage itself will be attached to their existing garage (which is attached to ours and shares a flatroof) at the rear and attached to his bungalow along the other side.If it's a non-attached outbuilding, probably not. If it's brick construction it will be constructed of substantially non-flammable materials, and with an external size of 6 x 5.5 it is likely to be 5.6 x 5.1 or so internally which is under the 30sqm internal floor area where building regs kick in.
I imagine this will require fairly substantial foundations hence my concern about the retaining wall.
Cheers.