Today I had to have a new gas feed pipe run into my house and have it connected to the meter. An engineer turned up and I asked to see his gas-safe certificate but he didn't have it with him so I asked him to leave. At 8 pm another engineer turned up and I asked him the same question but he didn't have it either. I then asked him for his seven digit number so I could check it out on the gas-safe register. He said he couldn't remember it, so I asked him his name so I could check it and see his photo online on the same register. He seemed to have a problem remembering his name but finally gave me it. Unsurprisingly he wasn't registered so I told him to leave. I had spoken to someone at Gas-safe earlier and they told me if I didn't have the engineers number and something went wrong any insurance could be invalidated because I had allowed an unqualified person to work in my house.
Hopefully, this thread will serve as a warning to other forum users to always check a tradesman's qualifications before allowing work to be carried out because the consequences could be dangerous and very expensive if anything goes wrong.