I have just tried NR's quote system - they are only offering electric for me. I'm on a dual fuel tariff with Outfox, which I have been on since a year last November. I normally look to switch around November, using MSE's Cheap Energy's recommended cheapest dual supplier. MSE emailed me in October suggesting it would be worth switching to another tariff with Outfox, so I switched, then noticed the newer tariff was slightly more expensive. MSE then sent a second email to say there had been a glitch in the calculation and it was wrong, but too late - I had already switched.
The switch locked me into a contract until next October, but I'm not now complaining - MSE's cheapest quote now is £100 more per year than I will pay, so lucky error.
For those who can carefully control and adapt when they use the kwh, I understand Octopus offer an hourly variable tariff, where sometimes they pay you to use surplus power, charging more during peak demands. They give a few hours notice of when the cheap and expensive rates will be.