A group of Tory MPs is planning to warn the Treasury against a mooted rise in fuel duty at the budget, amid wider alarm within the party that Boris Johnson and Rishi Sunak are prepared to raise taxes on 11 March.

Backbench MPs plan to write to the chancellor calling for a fuel duty cut or freeze and highlighting Johnson’s claims during the election campaign that he had “no intention” of raising fuel duty, which was repeatedly frozen during George Osborne’s years as chancellor.

The plan under consideration is an inflation-linked rise of about 2p a litre, although this might not be implemented until next year.

Tories are worried that an increase in fuel duty would go down badly with voters outside cities who use their cars to get to work. It comes on top of other recent tax-raising budget ideas that appear to have come out of No 10 and 11.

Howard Cox, the co-founder of the Fair Fuel campaign, said he had been told an increase in fuel duty was under consideration, driven by Johnson’s senior adviser, Dominic Cummings, before the Cop26 climate summit due to be held in Glasgow in November. Cox said it would “hit lower-income families” and predicted a huge backlash among Tory MPs.

Robert Halfon, a Conservative MP and former minister who has long led a campaign for fuel duty cuts, said: “The whole of this last election was about looking after working voters, blue-collar voters and helping with the cost of living. A fuel duty rise doesn’t just impact motorists but hits food prices, public services, ambulance costs and business costs and could have an impact on employment. It could also increase the price of bus fares because a lot of them use diesel. People think it’s just a motorists’ issue but it isn’t.

“I’m sure that millions of working people watching Boris, trust Boris when he said at the election he had no plans for a fuel duty increase.”

A string of Conservative MPs and commentators have reacted angrily to the prospect of possible tax rises in recent weeks, including the idea of a mansion tax, revaluation of council tax bands and cuts to pension tax relief.

Johnson’s manifesto did not signal any of those as a possibility but only explicitly pledged not to raise VAT, income tax or national insurance.

However, Tory MPs are sceptical that these will really come to pass given the likely outrage among the party’s traditional older, wealthier voter base.

One Tory MP said: “You just don’t know whether they’re trying to fly kites. I can’t see the pension thing happening. I think it will affect savings and the pensions industry, and our voters won’t like it.”

The other possibility is that No 10 is floating a number of possible tax rises in order to soften up Tories about the idea of loosening constraints on borrowing as an alternative. Sajid Javid, the former chancellor ousted by a ploy to sack all his advisers, was opposed to weakening his own fiscal rules just months after setting them at the election.