And while we're on the subject.....
I'm afraid that I have had several bad experiences with so-called "Gas Engineers" in the past, both during the Gas Safe era and previously under the CORGI system. As a practicing Engineer myself, I would never trust a technician who is licensed under either CORGI or GSR to do a proper job.
In one case, a relative had their gas fire serviced under a British Gas scheme, and afterwards noticed a smell emanating from the fireplace. On taking the front cover off the fire, I discovered that the main gas supply pipe was only finger tight, the fitter had not checked his work after reassembling the fire. A quick pinch up with the right sized spanner rectified the problem.
In another case, a neighbour had a new gas fire fitted by a GORGI registered fitter, and some years later, whilst undergoing a yearly service by a GSR registered fitter (not the same one), it was discovered that the fire had not been fitted correctly, and was spilling Carbon Monoxide into the living room. This second fitter disconnected the fire and slapped a red sticker on it, to say that it had been condemned. After several attempts to get yet another fitter to go and rectify the situation, the fire is still out of service, as no-one will touch an appliance that has been condemned by a different fitter, and the fitter who condemned it won't touch it because he didn't install it in the first place. So my neighbour has been without a living room fire for the last 13 years.
And gas fitters aren't the only ones who can be incompetent. I once had electric storage heaters installed by a registered electrician, but when the electricity company inspector came to inspect the installation, he refused to pass it because it did not have its own Earth Leakage Trip in addition the the existing one for the rest of the house. The installer came and added the ELT, but that was again condemned by the inspector because the installer had insisted on bypassing the ELT with a solid earth, thus rendering both ELTs inoperative. A three week long argument (in Slow Motion) ensued between these two bodies until I took the law into my own hands and removed the offending earth wire. Next time the inspector came, he was satisfied, and passed the system.
I have worked in several different departments of a large electrical engineering company, and unless you know your stuff, you don't last long in that sort of environment.