Guardian News and Media/London

Energy providers are battling to offer the longest fixed-rate tariff as the summer months come to an end, ahead of expected price hikes for consumers.

Price comparison website energyhelpline.com warns that the average household energy bill could rise by up to £142 over autumn, with energy companies looking to raise bills by between 5% and 10%.

However, there is a growing range of deals enabling consumers to lock in to today’s prices.

Scottish Power launched a new longest-term fixed tariff last week, at an average of £1,350 a year for gas and electricity until January 2017. This comes with a £10 donation to Cancer Research UK on taking out the deal, with a further £10 a year donation until it ends - a total of £40 if you signed up today. It comes with exit fees of £50.

Lucy Darch, head of energy at MoneySuperMarket.com, says: “Saving money and choosing a tariff that meets your needs is key. If you do like the thought of donating to charity you may want to consider making your contribution directly.”

The Scottish Power tariff is the same price as EDF Energy’s Blue + Price Freeeeze, which offers fixed prices until November 2016, although this deal comes with no exit fees.

However, the deals with the longest terms are not the cheapest on the market. MS Energy Fix and Save, at £1,139 a year until September 2014, is the lowest priced tariff available currently, according to uSwitch.com. This is £211 a year cheaper than Scottish Power’s new plan, and comes with a £50 cancellation fee.

The second cheapest is npower’s Online Price Fix October 2014 at £1,181 with no cancellation fee. Darch says: “A fixed deal is definitely the right move to make it just depends how long you want to safeguard your prices.”