Evening Golden Oldie,
Well I'm no expert but I believe that you can switch at anytime as long as any outstanding bills are paid or 28 days after 'coming on line' from a previous provider. Try the gas and electricity forum here for providers in your area. You may find that Dual fuel, direct debit and internet tarriffs gives you the greatest savings plus on this site certain switches will give you a further £30 cashback. I agree with the rise in fuel prices it's a good time to switch right now especially if you haven't done so for a while. IMO however I find cheapest is good but read reviews of the providers Customer services there's no point going for a cheaper tariff if you spend ages at Customer services trying to resolve problems.
Best of Luck!
Paul