Despite recent price cuts, customers on standard energy tariffs are paying far more than they need to for gas and electricity.

When a dozen of the most popular fixed-rate deals expire at the end of this month, thousands more will join them.

Last month, the Big Six providers announced reductions in their standard gas prices, but in most cases fixed-price tariffs remain a much cheaper option, and anyone on a standard contract should be considering a switch.

This also applies to those whose fixes are about to finish, as they will be automatically transferred to a standard tariff if they don't act. And even customers on fixes with time to run could find it worth paying exit penalties to move.

The Big Six's gas price cuts range from 5.1 per cent at Npower to 1.3 per cent by EDF, making minnow Ovo Energy's recent reduction of 10.4 per cent seem generous.

However, with wholesale costs down 37 per cent on their April 2013 peak, none of these changes will dent industry profits.

Jeremy Cryer, energy spokesperson at comparison site Gocompare.com, said: "The major companies stand to make nearly 50 per cent more profit this year from UK households. Coming off the back of falling wholesale gas prices, this will come as a major slap in the face to consumers."

Only E.ON's 3.5 per cent cut took effect immediately. ScottishPower, British Gas, Npower and EDF chose to make consumers wait until this month, while those with SSE won't benefit until the end of April.

Stephen Murray, energy expert at MoneySupermarket.com, said: "It's been frustrating to see all but one of the Big Six choose to delay a cut in prices. They have all ensured they gain a few extra weeks at higher prices when energy consumption remains high in the colder weather."

Meanwhile, despite falls in wholesale electricity costs over the past year, none of the Big Six have passed these on.

Good Energy, which came second in a recent customer satisfaction survey by consumers' organisation Which?, is unusual in reducing its electricity price by 2.1 per cent alongside a gas price cut of 3.2 per cent.

Despite the cuts, according to Gocompare.com, customers on 11 out of the 12 fixed-price dual fuel deals ending this month face an average annual price rise of 6.7 per cent, or £69, if they accept their supplier's standard tariff.

ScottishPower, British Gas, Npower, EDF, Sainsbury's Energy and M&S Energy all have deals expiring on February 28. ScottishPower has five.

Only users on British Gas's Fix and Fall February 2015 tariff will see costs drop. Its new standard tariff is 5.7 per cent cheaper, making a £37 annual saving for a medium use, dual fuel customer on monthly direct debit.

The biggest losers will be those on Npower's Online Price Fix February 2015 and Sainsbury's Fixed Price February 2015, who will pay an average of £117 and £101 more respectively.

For other medium users, rises are likely to be around £55 - for heavy users they will be much more.

Once the gas price cuts take effect, the Big Six's average standard cost will be £1,159. Anyone determined to remain on a standard tariff would be better off with Ovo, which will charge £1,051 after its gas price falls on March 1.

Taking another fix is likely to be much more cost effective though, with the current top ten deals costing between £913 and £932 for a medium use, dual fuel, monthly direct debit customer.

On this basis, someone moving from Npower's new standard tariff of £1,170 to Extra Energy's Fresh Fixed Price February 2016 v1 would save £257 a year.

Eight out of the top ten fixes charge early exit penalties, typically £25 to £30 per fuel. However, these don't apply once the supplier sends notification that the tariff is about to expire. This usually happens six or seven weeks before the end, and switches after this are free.

Anyone on a fix that currently has longer to run may still find that, with so many new tariffs available, it is worth paying a penalty to move on.

Those more comfortable with a fully penalty-free deal could sign up for Npower's Price Fix May 2016 at £927, or ScottishPower's Online Fixed Price Energy February 2016 costing £930, and still save well over £200 on the equivalent standard tariff.

Many people are nervous about switching supplier, but for most it is a straightforward procedure. And it has become far less confusing since regulator Ofgem limited firms to a maximum of four tariffs per fuel.

Anyone particularly concerned about service as well as value might want to look beyond the major players.

In the Which? survey, SSE and E.ON did best of the Big Six at 12th equal with a 50 per cent satisfaction score, while Npower was last at a dismal 18th, scoring only 35 per cent. The top five spots went to Ecotricity, Good Energy, Ebico, Ovo and Utility Warehouse.

Mark Todd, director of comparison site Energyhelpline.com, said: "If you don't switch, only your energy supplier will get rich. Switching is surprisingly simple, taking just five to ten minutes on a price comparison site, so it couldn't be easier to make important savings."