Millions of families face soaring energy bills after a third ‘Big Six’ firm in a week announced price rises.

It follows watchdog Ofgem’s decision to increase its energy price cap by an average £117 last Thursday.

Npower said yesterday it is raising prices by 10 per cent for around one million gas and electricity customers on its standard variable tariff from April 1.

Npower said yesterday it is raising prices by 10 per cent for around one million gas and electricity customers on its standard variable tariff from April 1

They will now pay an average £1,254 a year – an extra £117. Eon and EDF Energy had earlier announced they would also hike standard plans to £1,254 from the same date.

It is the maximum they can charge under the new cap. A total of 4.1million Npower, Eon and EDF customers are set to be affected. Ofgem originally set the cap at £1,137 on January 1. It was supposed to protect 11million loyal customers on standard variable tariffs from being ripped off. Households were promised annual savings of £76 at the time.

But just over a month later Ofgem revealed the cap would rise by £117 to £1,254 on April 1 – wiping out any previous savings.

The increase has been blamed largely on rising wholesale costs of gas and electricity.

Stephen Murray, energy expert at Moneysupermarket, said: ‘Barely is the ink dry on Ofgem’s announcement of a whopping £117 increase than half of the Big Six have moved their default prices up to that figure.

‘The others seem sure to follow, meaning 11million households have higher bills waiting for them come April 1.’

Eon and EDF Energy had earlier announced they would also hike standard plans to £1,254 from the same date

An Npower spokesman said: ‘Ofgem has increased the level of the standard variable tariff price cap by £117 in response to increased costs being faced by the industry.

‘Therefore Npower will be mirroring the full level of the increase from April 1.’

Comparison site uSwitch said the increase means customers will be paying around £294 more than the cheapest deal on the market.

Rik Smith, energy expert at uSwitch.com, said: ‘These announcements are coming like clockwork, shattering the myth that the cap is guaranteeing a good deal for customers on standard tariffs.

‘It’s vital that households don’t fall for the price cap con. Since Ofgem announced last week that the level of the cap was going up, over four million customers have already been handed a £490million confirmed bill increase, kicking in on April 1.

‘Unfortunately this number is only going to get bigger.’

A further review of the price cap is expected in August.