a conservatory this size would be subject to building regulations - have a read of:
http://www.conservatories4uk.com/bui...egulations.asp
I doubt the builder will accept any responsibility - it is the homeowners responsibility (in law) to make sure all permissions are obtained (both planning permission and building regs) That said - It is just about impossible to think any builder could have not known that building regs was required.
Different people will give different advice - but personally I would query this with your local council building control dept. (You could also perhaps have a word with a building surveyor or architect)
It is very hard to get Building Regs approval in reverse - so you are right - things do not look good.
It would be interesting to know the final outcome so please do keep us informed.
Good Luck and Best Wishes
CWGOD