Thanks mate, just think I've solved the problem. On Saturday I got the new HTC One as an upgrade, and Orange sent me out a new sim card, but there was nothing wrong with my old one so continued to use that. Was working perfectly until 15 mins ago. Put my new sim in and that works. I'm guessing they've cancelled my old one. Cheers for the reply though mate.
Personally I wouldn't touch it with a barge pole but I suppose it all depends on usage, I drive all over the country and often find myself without service
Bossman seems like he is much more of a traveller than me so I would take his word. However, at my place of work I used to be on O2 and I got a terrible signal. Since joining Orange I've had no trouble anywhere I have been. I don't get very far tho lol.