Two out of three households are overpaying for gas and electricity. Many regularly throw away hundreds of pounds a year simply because they have stayed too long on the same tariff, while others face a rise of 25per cent on their next bill.

Figures from Ofgem show that 8per cent more customers moved to a new supplier in the first three months of 2016 than during the same period last year, with the majority shunning the traditional Big Six.

Rachel Fletcher, the energy regulator’s senior partner for consumers and competition, said: “It’s encouraging to see a continued rise in the number of people switching, and an increasing number of suppliers entering the market.”

However, many other households are missing out. Ofgem calculates that around two-thirds could make significant savings by moving from their supplier’s expensive standard tariff to the cheapest fixed-term deal.

Ms Fletcher said: “There has never been a better time to switch suppliers and you could save up to £325, according to our latest figures. It is easy to do and Ofgem offers impartial advice on switching through its Be an Energy Shopper website, www.goenergyshopping.co.uk.”

Website Gocompare.com says that for households on 11 of the 17 fixed tariffs that came to an end last week, failure to act could be particularly expensive. They will be automatically switched to their supplier’s more costly standard deal, bringing an average price increase of £152, or 16per cent a year.

Co-operative Energy, EDF Energy, Extra Energy, First:Utility, Npower, Sainsbury’s Energy and ScottishPower all have tariffs that expired on 30 April. Customers of ScottishPower’s Online Fixed Saver April 2016 face the steepest rise, averaging £220 or 25.5per cent.

Ben Wilson, energy spokesperson at Gocompare.com, said: “Springtime, and the warmer weather that comes with it, tends to be the time of the year where people start switching off their heating and stop thinking about their energy bills.

“While it’s easy to put your energy usage to the back of your mind when it’s at its lowest, not keeping on top of when your fixed tariff expires can be a costly mistake.”

Six of the expired fixed tariffs were more expensive than the provider’s standard variable deal, but with an average saving of just three per cent, or £33, customers could still do better elsewhere.

The recent news that ScottishPower, one of the six largest providers, has been fined £18million by Ofgem for customer service failings may also encourage more people to switch.

Peter Earl, head of energy at Comparethemarket.com, said: “The mediocre price cuts by the Big Six earlier this year were an attempt to stop customers leaving in their droves to smaller suppliers. However, this sort of poor service will only increase switches away from the larger suppliers.

“There were over 40per cent of switches away from the Big Six through our website in March, with one in ten people choosing to switch away from ScottishPower.

“So while the promise of cheaper bills remains the main driver for switching, good customer service is becoming an increasingly important way for smaller players to positively differentiate themselves from the bigger competition.”

Consumers’ organisation Which? says the top firms for service are Ovo, Good Energy, Ecotricity, Ebico, Utility Warehouse and Utilita, all scoring 75 per cent or above in its recent survey. EDF was best of the Big Six, with 55 per cent, while Npower came last on 41 per cent.

It is easy to compare prices and make a switch through a website such as those offered by Ofgem, Which? (http://switch.which.co.uk) or the leading price comparison engines.

An even simpler option is to register for a group switching initiative, such as the one run by North Lanarkshire Council. It is open to households across Scotland, who then benefit from collective deals negotiated on their behalf – the more people who register, the greater the organising authority’s buying power.

Des Murray, the council’s head of business with housing property, said: “Our scheme makes it quick and simple for everyone to save on their bills. The savings some people have made during our previous campaigns were incredible, with some saving as much as £800 per year.”

The latest cut-price offer is open until midnight on Tuesday 17 May. It costs nothing to register at www.northlanarkshire.gov.uk/switch or by phone at 01698 274526, and there is no obligation to proceed. All you need is a recent energy bill or statement.

Everyone who registers will receive details of the deal plus a calculation showing how much they would save by accepting. They can then choose to go ahead or to remain with their existing provider.

Ben Wilson, of Gocompare.com, said: “The energy market has been fundamentally changed by the arrival of new players. In recent years we’ve seen the biggest price war the market has ever experienced, largely fuelled by the newcomers.

“As a result, there is now an opportunity to change consumer behaviour for the better and get a generation of bill payers into the habit of shopping around and taking control of their energy outgoings.”

It took Katherine Hunter just a few minutes to save more than £400 on her annual gas and electricity bill.

The personal assistant, who lives in Glenboig, near Coatbridge, joined North Lanarkshire Council’s Big Switch initiative last year.

She said: “I’d heard it was really easy to do and I looked at the information on the council website. Sometimes people are put off making a change because they think it’ll take ages, but wasn’t a hassle in any way.

“I was with Scottish Gas for years and just paid my bills without thinking, but when I looked into it, I realised they were really expensive compared to the switching offer.”

The 12-month collective deal, which was open to households across Scotland, was provided by E.on.

Katherine said: “Switching made a massive difference. I’ll definitely look into doing it again this year to see if there are any more savings to be made. I’ve spoken about it to all my family, so they’ll be doing it too.”