Owners of electric cars could pay just £100 a year to charge them up overnight, say researchers.

A study by WWF, the conservation charity, found that motorists would spend £170 a year to charge their vehicle at home by 2030. However, “smart charging” — at times of low demand on the grid such as overnight — could cut the cost by £70. The typical annual petrol bill is £800, the study said.

Ministers are committed to phasing out sales of new combustion engine cars by 2040. Environmental groups want a more ambitious date.

The WWF study, carried out by the consultants Vivid Economics, found that meeting the government’s target would add £2.4 billion to the annual cost of running the electricity system.

Bringing the target date forward by a decade to 2030 would increase the total bill to £3.8 billion a year, but researchers said that the use of smart charging would almost halve the bill to £2 billion.