Michael and Agnes Lamb were already feeling the heat after receiving regular demands from British Gas for fuel they haven't consumed.

But the elderly couple were even more shaken when their latest bill arrived as they were ordered to pay a whopping £25,865.14.

And, under the heading 'British Gas – your energy experts', the letter revealed the charges covered just a six day period last October.

"I'm so worried. Nearly every day we get bills, at least once a week. I dread the post coming, especially when you see the latest bill," said Mrs Lamb.

"We couldn't be using this much gas – there's only the two of us in the house.

"My husband is 82 and I'm 71. He has asthma and a bad heart and with these bills coming in regularly it is making his asthma worse.

"I'm not in good health either and this has just stressed me more."

The couple initially used British Gas for power supplies when they moved into their Bluebell Rise home in Morpeth 18 months ago.

However, six months later they switched to npower, settling a £500 final payment to their previous supplier, and were confident that future bills would be paid by direct debit from their bank account.

But at the turn of the year they started receiving demands from British Gas for 'outstanding charges'.

The first bill was for £199, but amounts differed by the week and on one occasion the Lambs received a 12p cheque from the company, as well as a demand for £46.

Letters have also varied from straightforward bills to final demands and even the threat of legal action.

Yet when the couple have contacted the supplier they have been assured that they owe nothing.

"I have phoned British Gas twice or thrice and my daughter has rang up, even the Citizens' Advice Bureau has checked, and we have been told we don't owe a penny," said Mrs Lamb.

"I just want this all cleared up and to find out what we owe and if we are in debt.

"I don't think we are, but we need to make sure because this can't go on."

A British Gas spokeswoman confirmed the bill was a mistake due to an incorrect meter reading by an independent mains gas supplier when the Lambs' account was set up.

She said the couple have now been sent a cheque for £343.58 that was found to be due to them and they will be given a final account statement showing a zero balance.