OP I'm a structural engineer.
Have you had any professional advice (eg archicest, engineer, project manager) other than your surveyor? Apologies if this sounds blunt, but you sound like you might not be completely up to speed with the various aspects of the processes involved which a professional would have been able to advise on and oversee for you. I'm not trying to spend your money, just it sounds like this is stressing you out and has caused delays?
A couple of things...
As several people have mentioned, this is nothing to do with planning. Your neighbour has had his moment to air his concerns yet the planners have awarded consent nonetheless. Afraid that's tough on him.
The party wall system does NOT allow him to prevent you doing the work, it simply makes sure that there are systems in place to minimise any damage to neighbours and, if this does occur, correctly apportion blame. It's actually very much in your interest as it will stop the neighbout claiming against you without reason.
Subsidence...have you ever started work yet? From your description it sounds like it's the proximity of foundations which have caused you to come under the PWA. If you haven't started work then it's a bit early for him to start talking about subsidence. Sounds like this might be him trying to scare you at present, though is of course something to keep an eye on. You mention a beam and block floor on piled foundations - do you know what type of piles? These aren't commonly used in residential works unless there is poor ground or a deep excavation next door.
I know this has now moved on to did us sion of insurance - this is not unreasonable and I'd take it out. Your solicitor should be able to advise or any other building professional. Your surveyor should be able to assist if they haven't already.