UK health officials have warned the country's National Health Service is facing its worst day of disruption yet as tens of thousands of nurses and ambulance staff are set to walk out in support of pay claims.

Monday's industrial action - expected to be the biggest strike in the history of the NHS - marks the first time the two groups have staged stoppages on the same day during the current wave of disputes convulsing public services.

It prompted NHS Providers to urge the public to use emergency services "wisely" as it warned the whole service was approaching a "crunch point".

The Royal College of Nursing - which is staging two days of action - has said that it is calling out twice as many of its members than it did during earlier strikes in December and January.

Ambulance crews and call handlers will return to work on Tuesday but are then due to walk out again on Friday.

Unions in Wales largely suspended similar action after the Welsh government came forward on Friday with an improved pay offer.

Over the weekend, Business Secretary Grant Shapps sparked anger among the ambulance unions when he accused them of putting patient lives at risk by refusing to inform employers of details of their strike action.

NHS Providers chief executive Sir Julian Hartley said they understood why so many of their staff had reached a "tipping point" as he urged ministers to sit down with unions to thrash out a settlement.

He said 88,000 appointments had been already been cancelled as a result of the current industrial action, hitting patients hard.

"We're facing a crunch point. Monday's co-ordinated walkout by nurses and ambulance workers could see the worst disruption yet for the NHS," he said.

"We face a very real risk that tens of thousands more patients will have their care disrupted in the coming days by this double whammy of strikes, especially as they're coming right after a weekend when we know demand for care tends to build up."

Sir Julian said NHS leaders would do everything possible to ensure safe care and to minimise disruption for patients, and called on the public to think carefully before accessing services.

"It's vital that in the event of an emergency, people continue to call 999," he said.

Health Secretary Steve Barclay repeated his call for the unions to call off their action as he insisted the Government could not give in to above-inflation pay claims.

"The Governor of the Bank of England warned if we try to beat inflation with high pay rises, it will only get worse and people would not be better off," he said.

"I have held constructive talks with the trade unions on pay and affordability and continue to urge them to call off the strikes."

However, Unite general secretary Sharon Graham said he was "not telling the truth" as neither he nor Rishi Sunak had been prepared to discuss pay.

The Royal Nursing College's Patricia Marquis appealed to the Prime Minister to "come to the table" for pay talks in order to avert more strike action.