Under the Consumer Credit Act 1974 regulated credit agreements may allow you to cancel the agreement should you change your mind. Worth pointing out is that there is a cooling off period in which you can change your mind. Assuming you signed the agreement anywhere other than on the premises of the trader or creditor; and you discussed the credit face-to-face with the trader or creditor before you signed the agreement, then you may cancel the agreement.
Below applies in your case as it was signed at your home, it is still enforceable unless you cancel under the next paragraph.
As you are entitled to cancel the agreement, you must be sent a cancellation notice within seven days of signing the agreement explaining that you have the right to cancel the agreement. A cancellation form will be enclosed with the notice and you can use this (or write a letter) to cancel the agreement. Should you decide to cancel, the cancellation must be sent to the lender within five days of receiving the notice, preferably by recorded delivery.