Money Saving Expert website (Martin Lewis) has section on this. There are template letters for you to personalise and also an interest calculator. You enter all of the individual charges and it does the calculation for you - great. I have just tried to re-open a Hardship Claim with HSBC and wrote to them more than 40 days ago and filled in their 'Financial Hardship' booklet and sent that off too. No response whatsoever - I take this to be a guilty silence and am encouraged! Next stop the Financial Ombudsman.