Good luck finding that. I asked a similar questing a couple of weeks ago, for the same reason, no one seemed to know. It's a real pain to go through them one by one. I ended up with a company I'd never heard of, Neon Reef, cheapest standing charge and all in about fiver a month cheaper than the next best which was Octopus, also got a referral so both I and the referrer get £25 (If you choose them, and want a referral let me know
) Of course as soon as I put the switch in progress the current supplier is making counter offers, too late, I'm not interested.
Switched over this week without any issues, sign up and communication have been good, no idea what the other customer services are like, though having never needed any such service from any supplier I have nothing to compare to anyway. It's surprisingly not smart meter compatible so have to enter the reading monthly, that suits me I like to be aware of usage anyway.