When you switch your energy supplier to get a cheaper deal, it's likely you'll choose a fixed plan, which will expire after the fixed duration (often 12 months).
After a plan's end date, you'll be rolled onto the supplier's default tariff — often a more expensive variable plan that could be subject to price increases.
Under Ofgem rules, you can switch exit fee free if your plan is ending in under 42 days, or you've already received a letter from your supplier reminding you the plan is ending soon.
The recent spate of price rises to standard variable tariffs makes switching to a new fixed plan even more important.
Price rises from EDF, npower, Scottish Power, Co-operative Energy and First Utility are all due to land in the next few weeks and these hikes affect the plans are the plans customers are rolled onto off of fixed deals.