I would complain - I'm with EON and we had letters a while ago saying that they would be coming to change the meter - it said to either ring for a time that was convenient, or just wait until they turned up (I did the latter. When he came to stood on the doorstep, said who he was, showed me his ID and asked if I'd received a letter informing me that they'd be changed.
If he's turned up in the manner as you described I wouldn't have been happy at all.
I'd complain to eon, and poss even the police. If he didnt show you any id and you've never had a letter, then who's to say he was from eon? You hear of imposters like this all the time. He prob was genuine but i'd def complain to eon at least.
I had someone knock on my door and say they were here to read the meter - well we just HAD the meter read - I queried where he was from - turned out he was from the former electricity suppliers. I pointed out that they were not our supplier anymore - his response - but your name and address is on our list. I looked at the name - from tenants 2 years ago.
It was a dodgy way of getting the supply switched back to them, I think!
So complain away! And complain to the Ombudsman as well - they need to know that the companies are being dodgy (Watchdog on BBC as well, in case there's a lot of this happening!!!)
You said you saw meter services van. I would have thought that Eon would have displayed their logo on it. Did you get details of the van just in case? You're right to be concerned whether it was legit or not
How coincidental is this? i have just answered the door to a worker from Eon! Advised he was here to change the gas meter, did display an ID badge though and was in a red Eon Van with a red Eon uniform on. Advised him that we were not expecting him and have not received any correspondence, he said not to worry then and than he could not proceed with the fitting. He said that he will arrange for us to be contacted about it.