Annoying Neighbours

Tenancy Deposits

Hi All
Another problem of mine,just one thing after the other
I was wondering if anyone has had the same problem,i have a sunroom on one of my propertys and its really old and the builder suggested it came down and a new one was built in its place.the thing is its attached to next door neighbours wall and when we got all the stuff and the builder was ready to start,the neighbour has refused to let us put the new one up,he said we are not allowed to attach anything to his wall and what he would have to do is buid another wall,he is being very petty and its really stressing me out as the perspext roof is leaking and with all the rain we have had lately,the tenants toys etc are in that room and are getting ruined as she has too much stuff and nowhere to put them.

But my question is
Can the neighbour dictate to me what i can and cant do and who would i need to speak too to get this sorted out.
Also the wall in question had been painted before i bought it and he is going mad about that saying i have devalued his home(the bit wall it tiny by the way)can he sue me for this even though i bought the hse like this.
Thanks