There are other threads on this forum with more details about what specific terms need to be on the CCA for it to be enforceable (dependant on the date of the CCA).
If pre April / May 2007 CCAs were not always to the required standard, but the act has been tightened in 2007.
It requires
Name
Address
Credit limit (or stated variable)
Interest rates, amounts and dates of repayments. (need to check this specifically).
It needs to have a space for a signature, but I believe that they can comply with the requirements by supplying a copy of the CCA with this, but perhaps not having your signature.
Have a read of the other threads to find out more.
If you have now received your CCA from the catalogue, depersonalise it and put it online so that others can help you review it.
If the lender believes that they have an eforceable agreement they will not settle for a low % as they could sell the debt for this amount.
If it is uneforceable, in theory they could still sell the debt, the uneforceable just means they can't chase you for payment through the court.
Good luck
Sparky.