British carmakers, which have invested billions in electric vehicles, urged the government on Wednesday to get a grip on its climate policy following reports it might delay a proposed ban on the sale of new petrol and diesel cars.

After weeks of speculation over the key net zero pledge, several media reported late Tuesday that Prime Minister Rishi Sunak would push back the ban by five years to 2035.

He is expected to set out the policy reset, aimed at easing the financial burden on households but slammed by some critics as a weakening of Britain's climate targets, in a speech at 1530 GMT on Wednesday.

The Society of Motor Manufacturers and Traders (SMMT), Britain's main auto trade group, said the country should be a leader in zero emission transport, a goal that required "clear, consistent" messaging that gives car buyers confidence.

"Confusion and uncertainty will only hold them back," SMMT Chief Executive Mike Hawes said.

Ford, among Britain's biggest automakers with a global $50 billion commitment to electrification, said manufacturers faced "the biggest industry transformation in over a century".

"Our business needs three things from the UK government: ambition, commitment and consistency. A relaxation of 2030 would undermine all three," Ford UK Chair Lisa Brankin said.

Peugeot and Vauxhall owner Stellantis, Tata Motors-owned Jaguar Land Rover and Volkswagen UK issued separate statements calling for policy certainty.

Speculation over the government's position on its green pledges grew after Sunak's Conservatives, trailing in opinion polls, narrowly won a by-election in July mainly because of local opposition to a low emission zone.

Since then, Sunak and his ministers have repeatedly backed the 2030 ban, with Transport Secretary Mark Harper confirming the pledge to an auto industry conference in London as recently as Monday.

"Moving this date for short term electoral gain will risk both the entire energy transition and the UK's international investment credibility," British electric vehicle campaign group FairCharge's founder Quentin Willson said.

The car industry has also bemoaned the lack of clarity over the government's zero emission vehicles (ZEV) rules, which had called for an increasing proportion of a manufacturer's sales to be ZEVs in the run up to 2030.

($1 = 0.8083 pounds) (Reporting by Sachin Ravikumar Editing by Mark POtter)