If you don't like what you see, you can walk away (I presume you are "sale agreed subject to survey")
If I was selling and you asked me to do repairs, I'd tell you to get lost to be honest. I am not aware of any obligation on the vendor- the house probably met the regs that were in place when it was built.
Have you had many surveys done? The first few always look very scary but when you've seen more you realise that there is always something that sounds bad but is (usually) easy to fix.
I would not show the survey to the vendors unless they were going to pay for it.