Switching lenders may sometimes lead to early repayment charges. If your early repayment period has not come to an end before you decide to remortgage, you may be charged with a fee. The only way to avoid the early repayment charge is to wait until the deal ends. In some cases, the benefits of remortgaging to a more attractive deal may outweigh the charges incurred by exiting the current deal too early.
It is always worth getting advice from an independent mortgage broker before you make the decision though.