BRITAIN'S 'Big Six' energy suppliers will all hike their prices on Monday, a watchdog has warned.

Gas and electricity firms are pushing their bills up to within £1 of a new cap which comes in to force on April 1, Which? said.

Regulator Ofgem has raised the controversial price cap for a nominally typical dual fuel bill by £117 a year, to £1,254. Which? said householders could end up paying £1 billion more a year in total.

VIDEO: The £1 billion cost of the great 'price cap' energy bill hike

More than 10 million homes are still powered and heated by energy sold at default standard tariffs. Critics believe the cap, which was designed to stop rip-off bills, has been ineffective.

READ MORE: Cap branded con as energy prices rise

Which? stressed there were still cheap deals around for those who shop around and avoid the standard tariffs subject to the cap.

Natalie Hitchins, Which? Head of Home Products and Services, said: “Many people who hoped the price cap would bring an end to unwelcome price increases will be left reeling after price hike Monday adds more than one billion pounds to their energy bills.

“If you are one of the millions of energy customers stuck on a rip-off standard variable or default tariff, our advice is simple - switch as soon as possible.

“There has been a recent rise in the number of cheap deals on the market - so you could choose better customer service while potentially saving more than £300 a year.”

Which? has identified 31 deals costing less than £1000 a year for a typical home. The cheapest deal, it said, was now £925 a year for a medium user willing to go 'paperless'.

Ofgem earlier said it had increased the cap in the light of rises in wholesale energy prices. A new provider, Bulb, earlier this year accused bigger operators, including SSE and Scottish Power, of working like a cartel because their prices were so similar. Industry leaders rejected this interpretation, saying similar prices were an "unintended consequence" of the cap.

Mobile phone bills and TV subscription costs set to go up at 2.6 per cent and 5.1 per cent respectively today. Digital TV provider Freeview said a survey had found people thought they were spending £29 on monthly subscriptions – but we’re actually paying £149.