Sainsbury’s Energy has launched the longest fixed price tariff on the market, protecting customers from price hikes for four years.

The new plan means customers can lock in prices until the 31st of March 2018 – three months more than what is currently offered by npower. However, customers will have to pay £50 per fuel if they decide to switch before the fixed period is over.

It will cost the average householder £1,316 – just £52 more expensive than the average standard energy bill from the Big Six, comparison site uSwitch claims but is £300 a year more expensive than the cheapest available tariff on the market.