I stood with the electrician whilst he checked everything thoroughly. I was working on the house in the same room for the whole day. He checked everything thoroughly and what he did was considered legal, safe and acceptable by Building Control, so I'm not worried in the least. But thank you for the concern.
What did he say about the lack of grommets?
He said that grommets should be installed in all new back boxes, and that he was happy to see that I had fitted them to all the newly installed sockets and switches.
As this main light switch had been in place since I moved into the premises almost 10 years ago and the wiring was only re-used for the new lighting he said that it did not have to have grommets fitted (although it was advisable) as the switch and it's metal back box hadn't been touched by me.
Hopefully the issue, that is completely resolved, can now be left alone and laid to rest.