I feel your pain. We had a nightmare with our next door neighbour a few years ago regarding a side return extension. Ultimately it ended up with solicitors (we won) but it cost us a lot of money in legal fees, a lot of time and a lot of tears and sleepless nights. She was so unreasonable. It still makes me cross to this day!
Please be really careful before starting any work. I wouldn't want anyone to go through what we did.
You need a good party wall surveyor. We are currently using a guy called John Soulsby on another project, and he has been great. We have 7 next door neighbours(!) as the houses have been divided in to flats and the process this time around has been pretty seamless. This may be down to the fact that this time around we have much nicer, more reasobable neighbours, but even so I think he knows his stuff.
johnr.soulsby@ntlworld.com