Actually, one of mine does almost that. Egg Money pay me interest at 4% on positive balance (of which I get about 80%, or nett 3.2%, because the revenoo take tax on it), they charge about 13% on negative balance. This means that they actually pay me more interest than any of the savings accounts I have! Oh, and they pay me 1% "cashback" on every purchase with it (credited once a year; I got around 15 pounds back last month). So I keep it in credit and am thinking of transferring some of my savings onto it to get more interest...