Check the council regulations for fencing and their requirements for submission of plans and subsequent approvals. That way you can establish if the structure is legal. Legal representation may be required. I would have thought that any footing is shared equally between the two properties. Sounds like the neighbour is trying to bluff his way through. Another thought as well, is to have the boundary surveyed as it wouldn't be the first to be incorrect.These can turn a bit ugly as some councils don't want to get involved, but if there a clear defined rules and regs. for boundary fences then the council is duty bound to enforce their own policies.
I know if it was me, I wouldn't take it lying down!
Maggsie

