The firm said that, on average, residents of Southall in North-West London owed 30% more than the national average, with long term problem debts of £3,618. The UK's average balance is £2,759.
The figures do not refer to consumer debt, but rather debt that has remained unpaid and has been sold on to recovery agencies. The company defines long-term problem debt as: "Debt repayments that individuals have defaulted on for a considerable period of time - in most cases this will have been months or even years. Consequently the debt has been sold onto a debt collection agency. The debt can be anything from credit or store cards repayments to repayments on car or home improvement loans."
The top – or should that be bottom – five national postcodes in terms of long term problem debt balances were all found within London suburbs.
In Harrow, average balances were £3,570, in Ilford £3,587, while Croydon saw average balances of £3,472 and in Kingston the figure stood at £3,391.
Bristol – £ 2,806
Edinburgh – £ 2,779
Glasgow – £2,696
Birmingham - £ 2,626
Cardiff - £ 2,522
Manchester - £2,410
Leeds - £ 2,389
Newcastle – £2,356
Liverpool - £ 2,222
Belfast (Northern Ireland) - £1,584
Bob Kingdon of 1st Credit said: "While there are all sorts of reasons why people struggle to repay their debts, failing to gain control of personal finances is a problem faced by people all over the UK. That's why it is so important to understand that the best solution is always to tackle debt head-on.
"The way to do this is to face up to the problem by talking to the company that holds your debt and agreeing a repayment plan that you can manage. An important part of this in our case is that once we own the debt we don't charge additional interest, so from day one you can reduce the amount you owe and are one step closer to your debt-free day."