Logically, 0% rates are there to save money. If you chose to pay the minimum, ie £5 per month with a high balance then you made a calculated decision not to take advantage of saving money. Therefore I suspect that you are a rate surfer. In your T&C's interest rates can be increased or decrease as they are variable unless you sign up for a fixed for life deal.
Your interest rate will be calculated on risk, conduct and credit search reviews, which will be silent therefore leaving no footprint, this also is in your T&C's. There are a number of factors included in this. Be thankful you 1. Have a credit card, 2. Still have a credit limit as another company reviewed all it's high risk accounts the back end of last year and withdrew the non profitable accounts and their high risk accounts after reviewing the strategy.