I come under Eastleigh Borough Council and all planning applications can be viewed online. I have also read that there rules state that no part of an extension or new build can overhang another property. Planning permission can be granted for your property by someone else, it does not mean they can build on your property.
For example you have a large property and builder enqures to buy your house, he can apply for planning permission for what he wants to do, and he may get planning permission. It does not mean you have to sell your property to the builder.
I suspect the architect/builder/council/building regs have made a big mistake here, Have you tried a no win no fee solicitor ?
If it where my house I would give 14 days to remove anything on my property, then I would remove it myself, carefully and causing as little damage as possible. I suspect this would be when the police would arrive. They cannot stop you doing work to items on your property so long as you are not endangering anyone.
I had a similar issue many years ago. I put up an extension, and when measuring, my neigbours conservatory roof was overhanging my side, I gave him the 14 days notice. and then I removed the offending bit. We never spoke again. But I did hand the bit back undamaged, and carried on with my extension. I watched him very carefully when he fixed his roof.
Good luck, and don't give up if you are right. There are far to many people out there who try to take advantage of people, and this is what they have done to you.
Just looked at your local council planning site, it looks very poor to me. Like they don't want to give out information.