Trade unions on Wednesday vowed to boycott the independent review body examining a wage settlement for NHS staff in the UK for the coming year, as ambulance workers staged fresh strikes over pay.

A total of 14 unions representing more than 1mn NHS staff made clear they would not co-operate with the review body process and called for direct negotiations with ministers to resolve their pay dispute.

In an effort to end the worst wave of UK strikes in decades, Rishi Sunak last week sought talks with unions about the evidence both sides will submit to public sector pay review bodies that will make wage recommendations to ministers for the financial year starting in April.

But the unions have strongly criticised the review body process, and demanded ministers improve the pay of workers for the current financial year or face the likelihood of prolonged strikes.

Wednesday marked the deadline for the submission of evidence to the health service pay review body for the 2023-24 wage round.

Sara Gorton, chair of the NHS group of unions and Unison head of health, said only direct talks with ministers, backed with new funds from the Treasury, could end industrial action.

Unison and the GMB were the health unions that organised strikes by ambulance workers on Wednesday in England and Wales, as well as last month.

“The next strike is almost two weeks away,” said Gorton. “Ministers should use the time well between now and then.” The GMB said it would meet on Monday to discuss further potential strike dates.

Sharon Graham, general secretary of the union Unite, which also organised the ambulance worker strikes last month, called for the abolition of the NHS pay review body, suggesting it had served as “a smokescreen which has allowed government to drive the NHS to the point of collapse”.

Sunak told MPs the government wanted a “constructive dialogue” with unions, while health secretary Steve Barclay insisted “nothing is off the table” in relation to pay.

Chancellor Jeremy Hunt has not excluded ideas being considered by Barclay to resolve the NHS strikes, including a one-off lump sum payment to health workers or backdating the 2023-24 pay award to January 2023.

“Nothing is ruled in or out until we have seen what is actually being proposed,” said one Hunt ally.

However the Treasury blocked a lump-sum payment to NHS staff before Christmas and is insisting any new pay deal for public sector workers is funded from within existing Whitehall departmental budgets.

Meanwhile, amid criticism by unions that Sunak does not understand the pressures facing the health service, the prime minister said he was registered with an NHS general practitioner.

At the weekend, Sunak had refused to disclose whether he used a private GP. On Wednesday, he told MPs he had used “independent healthcare in the past”.

There were signs the latest strike by ambulance workers had prompted the public to make fewer 999 calls.

Saffron Cordery, interim chief executive of NHS Providers, which represents health organisations, told the BBC that, as had happened during the last strike in December, “we have seen, on ambulance strike day, reduced demand for ambulance services”.

Both the Yorkshire and Wales ambulance trusts confirmed that, by Wednesday afternoon, they had seen fewer 999 calls.

The PCS union, which represents civil servants, announced a significant escalation of the industrial action it is organising over pay and other issues by calling a strike by 100,000 members at 124 government departments and other public bodies.

The PCS said the action on February 1 would be the largest by civil servants for years, and would coincide with a day of protest against the government’s new anti-strikes legislation.

Mark Serwotka, PCS general secretary, said the dispute could be resolved if ministers put more money on the table at a meeting on Thursday but otherwise the union would not “stand by as hardline Tory MPs . . . tell our hard-working members they should be grateful to have jobs”.

Union leaders warned there had been almost no progress in negotiations with employers to try to stop more strikes on the railways.

“We are further away than when we started,” Mick Whelan, head of train drivers’ union Aslef, told MPs. Mick Lynch, general secretary of the RMT transport union, said he could not “see a landing zone” in discussions with train companies.

Steve Montgomery, chair of the Rail Delivery Group, a trade body, conceded there were “challenges” in finding a pay deal with drivers.

Tim Shoveller, an executive at infrastructure operator Network Rail, said there was “every chance” of a deal with the RMT.