Low-paid health and care workers are calling in sick because they cannot afford to fill their cars with petrol to travel to work, the head of the UK’s largest trade union has warned.

Boris Johnson said on Thursday that the UK economy was “steering into the wind” but cautioned against a “wage-price spiral”, as the cost of a tank of fuel hit a record £100.

Christina McAnea, general secretary of the public services union Unison, said some of her members were likely to strike in the coming months, faced by real-terms pay cuts as the cost of living crisis bites.

“[Petrol price rises are] having a big impact on people with jobs that mean they have to travel. So community health workers, health visitors, care workers, social workers … are saying they just cannot afford to do their jobs any more,” she said.

“We’re actually hearing of people who would rather phone in sick because they don’t have the money to fill up their cars and do their jobs. And more and more people are leaving public services, even in local government. There’s huge vacancies across local government.”

She said of the prospect of strike action: “We don’t want to bring low-paid workers out on strike. But if there’s no alternative, what else can people do?

“If we’ve got a government where they are getting 2-3% pay increases and we’ve got inflation running at 10% or even more by the end of the year and they already pay a disproportionate amount of their income on fuel, housing, energy and food costs, if you are low paid worker … that has a huge impact on people.”

McAnea, who was a housing officer in Glasgow before becoming a full-time union official, said Unison is already balloting local government staff in Scotland over industrial action, which could lead to schools being closed.

“We don’t want to inconvenience people and we know that has a huge impact on people. But there comes a point where there’s no alternative,” she said. “The same thing could happen in England and Wales. I’m not saying there will be strikes tomorrow, but there’s a lot of anger out there, and people become more desperate.”

Her warning came as train strikes by member of the RMT union are expected to cause travel chaos later this month. Two other unions representing drivers and support staff, Aslef and the TSSA, are also considering industrial action later in the summer, raising the threat of a complete national shutdown.

The prime minister has previously pledged to transform the UK into a “high wage economy” but he warned on Thursday that matching wage rises to inflation in the current circumstances risked a 1970s-style “wage-price spiral”.

Thinktank the Organisation of Economic cooperation and Development (OECD) warned this week that UK growth could grind to a halt next year, making it the weakest developed economy aside from Russia, but with inflation still painfully high.

Ministers are expected to announce a raft of public sector pay deals in the coming weeks, including for nurses.

In evidence to the NHS pay review body earlier this year the government said there was “extremely limited room for any further investment in pay” and that “financial restraint” was needed.

The TUC is warning that pushing through the 3% settlement the Department of Health and Social Care has suggested would amount to a £1,600 real-terms pay cut for nurses, with inflation running at 9% and expected to go higher.

Alongside the GMB and Unite, Unison submitted a pay claim for local government workers, including school staff in England, Wales and Northern Ireland this week, asking for a pay rise of at least £2,000.

McAnea said: “Pay restraint is completely inappropriate when we are talking about people in local government. About 50% of workers in local government earn less than £25,000 a year.

“If you’re a care worker, if you do a job out in the community and you have to go and visit people, and it’s costing you £100 to fill up: not possible.”

Her warning came as Johnson urged petrol retailers to “be responsible” and “look after consumers”, amid concerns in government that the 5p reduction in fuel duty announced in Rishi Sunak’s spring statement was not being passed on in full to motorists.

“We are watching it, and of course we hope that corporations will be responsible,” Johnson said, as he delivered a speech about the economy in Blackpool.

Figures from the data firm Experian Catalist show the average price of a litre of petrol at UK forecourts reached a record 182.3p on Wednesday.

That was an increase of 1.6p compared with Tuesday, taking the average cost of filling a 55-litre family car to £100.27. The RAC’s Simon Williams called it, “a truly dark day today for drivers”.

It is understood ministers are examining the possibility of naming and shaming retailers that are taking advantage of surging global energy prices to increase their margins.

A government source stressed the measure had been used successfully before – with profiteering on Covid tests, for example – but warned it was more complex with fuel due to prices fluctuating at pumps as much as several times a day.

The business secretary, Kwasi Kwarteng, has already written to retailers urging them to behave responsibly, and asked the competition watchdog to examine at the issue.