As your extension was built 40 years ago, it does not have to conform to Building Regulations. It is surprising that a surveyor should make a comment such as this, as a competent surveyor should know better. For extensions and other notifiable work done after November 1985, the local Building Control department can give you a regularization certificate, confirming that the work as done complied with the Regs. in force at the time of construction (subject to the Inspector actually checking the work on site, and your payment of a fee). However, the local authority will not entertain looking at work dating from before Nov. 1985 (it's doubtful that any inspectors would even remember what the regs were in the 1970s!). In short, your extension does not have to comply with anything, and no one can insist that it should.