Around nine million energy customers of the largest firms could save up to £434 a year by switching to a better deal.

Four of the ‘Big Six’ energy companies – British Gas, EDF, Npower and Scottish Power – will raise, if they haven’t already, standard variable tariff prices in the coming weeks.

This means customers will pay up to £76 a year more. SSE customers will see the biggest price increase, averaging 6.7%, which will come into effect on 11 July. This takes the average dual fuel bill to £1,196 a year.

Overall, Npower customers will be paying the most as its price will increase by £64 (5.5%) to £1,230 a year from 17 June.

According to the Which? research, Npower customers can save the most (up to £434) by switching to the cheapest deal on the market. Utility Point’s variable tariff costs £797 per year but for those wanting to stick to Npower, asking to move to its cheapest tariff could save them £268.

British Gas’ price hike came into effect this week, with four million of its dual fuel standard tariff customers seeing their bill rise from £1,101 to £1,161 on average per year.

This is an increase of 5.5% or £60 a year – £364 more than the cheapest deal on the market. Householders keen to stay loyal to British Gas could still save £113 if they ask to switch to its best deal.

As of 1 June, Scottish Power customers on its standard tariff will see bills increase by an average of £63 a year (5.5%) bringing its standard tariff to £1,211 on average per year.

Affecting more than a million households, this increase will make its standard tariff cost £414 more than the cheapest deal on the market and £100 more than Scottish Power’s own cheapest tariff.

Over a million EDF customers will also be subject to a price increase of 1.4% or £16 a year for electricity on 7 June. This will take the SVT to £1,158 for the average user. Overall, EDF’s dual fuel standard tariff will be £361 more than the cheapest deal and £167 more than its cheapest available deal.

E.on hasn’t announced a price increase but earlier this year it said it was cutting dual fuel and paperless discounts from its bills and increasing its standing charge for some customers. This  means some users pay £30 more a year, taking average annual bills to £1,153.

Alex Neill, Which? managing director of home products and services, said: “Energy customers tired of being slapped with eye-watering energy bills can take the power back into their own hands and radically change how much they pay, simply by choosing a better deal.

“Before the energy price cap comes into effect later this year, anyone still suffering on a poor value standard tariff should take five minutes to compare and switch as they could potentially save up to £434 a year.”