One woman complained she hadn't had a gas bill for three years

Energywatch says that households are then faced with huge bills which are difficult for them to pay.

It is launching a campaign on Tuesday calling for more clarity on estimated bills and is expected to name the worst offenders.

Nearly half the 86,000 complaints received by energywatch last year related to billing and accounts.

It said it has heard of energy suppliers chasing the wrong customer for payment, of people being disconnected over "grossly over-estimated" bills and others being hassled by debt collection firms.

If you have been waiting a year you should be prudent and put that money aside British Gas

In February this year energywatch accused British Gas of "corporate apathy" after claiming the company had not billed some customers for their electricity supply for more than four years.

A spokesman for the company said it was sympathetic but warned: "If you have been waiting a year you should be prudent and put that money aside."

The watchdog is backing calls for all estimated bills to contain a clear warning to ensure customers know they can obtain their own reading which may be lower.

Ann Robinson, chair of energywatch, said: "Consumers tell us that inaccurate bills irritate them.

"That's why energywatch, as the consumer champion, will be launching a major campaign to tackle the problems that inaccurate energy bills cause consumers."

Electricity saving

Energywatch's campaign follows a report from the National Audit Office last week which suggested electricity companies had not passed on savings on wholesale prices to customers.

The report also found that households which stayed loyal to the company they bought their electricity from before deregulation of the market in 1999 were paying up to 22% more than those who switched supplier.

Energy giants Powergen, British Gas, npower and ScottishPower issued a joint statement in which they promised to tackle billing problems, particularly with customers wishing to switch supplier.