Your Halfords must be VERY......VERY different from Sheffield stores.Hello Betty. You could visit Halfords and ask them what you need. Some of their stores are very good and helpful, it clearly is a matter of luck. But they should be able to see what your system is and tell you what you need. I don't think that they will have what you need but they might be able to get it for you and fit it for you for a very reasonable price.
I'm lucky to have have good staff in the local store and they are one of the first places to go to for info
Staff round here don't know ATF from Turtle Wax
I concur with the doctor. Yes I do..Firstly locate the amplifier and take from it the part number any other useful information, then search the www and see what's around.
I doubt that any aftermarket amp will be compatible with the factory fitted head unit, assuming it is, and if one was found not without a lot of alterations to the system u have.