I think there's a planning law which says that you mustn't build within
3ft of a boundary (it's to allow you access for outside maintenance
without stepping on the next chap's land). I don't think it would apply
to a shed, which is a non-permanent structure (and certainly the garage
belonging to the neighbour at the end of our garden is only 6inches form
our wall), but it might be as well to chat over your plans with your
neighbour first, and get him on-side. Point out how much tidier this
will be than having a glory hole along the side of the house.
--

Thanks for the advice.

The neighbour in question has just put a shed about 5 inches from our fence.
Therefore I hope they will not mind if I do the same.