A clampdown on store card providers' exorbitant interest rates is expected to be announced tomorrow by the Competition Commission (CC).

It is expected to say, among other things, that the cards in question must display a highly-visible warning on monthly statements if their APR exceeds 25 per cent.

Two hoped-for consequences are that firms consequently reduce their rates – and that customers might be encouraged to search for better deals upon realisation of how much they are perpetually being charged.

It is also thought that the CC will ban the inclusive selling of payment protection insurance (PPI) in card packages – making it optional for those customers who wish to take out a store card.

Mike Naylor of Which? told This Is Money: "We welcome the moves but we think more needs to be done to give consumers the information at the point of sale rather than after they have taken the product out."

Better training for staff of the 70-plus groups offering store cards is also being pressed for, with calls abounding for them to be made aware themselves of the cards' charges so that they do not solely plug the fact that offers such as relatively minimal purchase discounts may be available.