Transferred to British Gas when my old supplier went bust. In the past 12 months I have spent just over £2000 with them, for my small one bed house which I occupy on my own. For around 3/4 months over winter I actually had my heating off, because I just couldn't afford the bills. I tried to transfer away from them but they blocked it. I have tried speaking to them about their bills.
Currently they are over the new guidelines for how much you can charge. Avoid them at all costs!