So sorry @JoannaDory that is so shit.
I don't think we are going to exchange this week either - we have been asking our sellers for a certificate for the (new) boiler since the start of the process. It was only installed 6 months ago (we are buying a completed renovation) and so we couldn't get an indemnity policy and tbh for a boiler that old I wanted the proper certificate.
They said the installer was going to register it with gas safe and would forward the certificate last week... and then on Tuesday they had a different plumber round who has now issued a certificate for the 16th February. The estate agent is being cagey but I suspect that the boiler was not installed correctly or the original installer was not gas safe registered and so a different plumber had to "install" it. Anyway, we now have the certificate and a report stating that it is safe.
BUT my solicitor friend who is dealing with our conveyancing has the next couple of days off. She has small DC like me and is absolutely on her knees with homeschooling and dealing with a massive workload due to the stamp duty holiday. So there is no way I am going to hassle or chase her.