JG: They have recently introduced stringent marketing rules in the UK, including this info. It hasn't had much effect on behaviour, and the industry hasn't minded much.
Problem is that it is of limited value given the complexity of the offers available. Issuers are struggling to differentiate a simple mass-market product in a competitive and profitable market with complicated tiered rates.
I have an offset mortgage, where my mortgage is a checking account with a big limit. When I worked in the department that managed credit risk across a multi-billion pound consumer portfolio, it took three of us - including two maths PhDs - twenty minutes to work out that the net interest benefit to me of taking the interest-free offer over the maximum period was £7, once we took into account differential interest rates and fees.
--James