The difference on energy bills between estimated meter readings and actual balances could force many families in to debt, as they receive “catch-up” bills of hundreds of pounds.

Families facing double digit increases to fuel bills could also be landed with the prospect of hundreds of pounds of additional charges, as estimated meter readings leave them short.

Households are advised to check their bills to see if they have only been paying the estimate or the actual meter reading, as companies could demand the difference in full, forcing many struggling families in to debt to find the extra funds.

Current legislation suppliers are required to take an actual meter reading once every two years, and even then the companies are only obliged to make “reasonable endeavours” to fulfill this, meaning the majority of bills rely on estimated numbers.

Customers who haven’t received a bill based on actual readings since September 2006 should double-check that their ‘catch-up’ bill is properly broken down, with all the charges being made at the correct price levels – not all charged at the current highest rate.

An Energywatch spokesman says: “You must pay for what you have used, but suppliers should not be charging any shortfall entirely at the increased rate.

“If there has been an increase in prices in that period, the demand in the “catch-up” bill should include the old and new rates. A supplier should charge you the energy you used at the correct tariff at the existing time, not just on the higher rate.”

Chiltern’s Nathan Gladwell says: “Over the last eighteen months there could have been three price increases, so it’s vitally important to ensure any potential shortfall is budgeted for.

“The impact of a “catch up” bill could push struggling households further in to the red on their overdraft or credit cards, especially when put alongside with other rising living costs.

“It may be necessary to arrange a debt repayment plan if this means that you are struggling to keep up with your current credit commitments.”