A cash-strapped couple from Eastville, Bristol, say it will take them three years to pay off a massive electricity bill they have mysteriously run up in their one-bedroom flat.

Kerry McDaid, 29, and partner John Judd, 27, who live in Clay Bottom, owe £1,190 for electricity between July last year and this month. The average electricity bill for a one-bedroom flat is around £500 a year.

British Gas have agreed to let the couple pay £70 a month for the bill and are sending a representative to the property to try and discover how the couple are using so much electricity.

Miss McDaid and Mr Judd say they can't understand how it could be possible to run up such a huge bill.

In the flat the couple have the usual white goods, one electric heater, a computer, electric cooker and a television.

Even British Gas admit the usage for such a small property is unusually high.

The couple, who have lived in the house for two years, got the bill after months of wrangling with the company to sort out an estimated bill that stated they owed £750 for two months, which, to their relief, was incorrect. British Gas has told the couple they can pay £70 a month which means, incorporating charges, the new bill will take three years to pay off.

Since the original dispute, Miss McDaid has had to give up her teaching course to earn money to pay the bills while studying for a PhD in contemporary history at UWE.

"It has been a complete nightmare," she said. "I have spent ages on the phone getting more and more stressed out.

"As far as I am aware we hardly use any electricity during the day because we are not in and if I am I usually only have the radio while I read a book – it just doesn't make sense.

"We have an electric heater in the lounge and bedroom but the one in the bedroom doesn't work so we don't ever have that on and we only have the one in the lounge on in the evenings if we need it. If the bill is correct it is a complete mystery how we are using so much electricity – there must be something wrong. We have agreed to pay £70 a month with British Gas but that will take us three years."

Mr Judd, who is studying for a degree in computer systems integration at UWE, said: "I have been really worried about people coming and taking our stuff away because they have threatened us with bailiffs.

"Things are bad for everybody financially at the moment and this is killing us – we hardly have any money as it is and it must be a mistake.

"It's making our lives a misery because it's always there hanging over our heads.

"It would be very helpful if British Gas could come out and show us what may be using so much electricity.

"It is a mystery at the moment because we are quite conscious of using electricity because Kerry is quite green so makes sure things are not on standby."

Sara Powell-Davies of British Gas said: "We are sorry that Ms McDaid and Mr Judd felt that they had to contact the media to resolve the issues they had with British Gas.

"We have checked their previous usage figures and are satisfied that the bills issued are correct. We have now agreed a payment plan with Ms McDaid and Mr Judd to pay off the outstanding amount and will also be giving them energy efficiency advice to help them reduce their usage.

"We always advise customers to check estimated bills and if they are incorrect, provide us with actual meter readings so that we can ensure they are billed for the correct amount."