Try contacting Environmental Health at your local council and ask them if
you have sited the heap correctly and if he has any grounds to complain.
If
you get in first, you'll have some amunition should they back you up.

Probably the LAST thing to do! Just ignore him and he will either go away
or go to the Council. In the latter case they will almost certainly tell him
to go away. Far better than letting it escalate.