Ambulance services face disruption and non-urgent caesarean sections and other elective operations will be delayed on Monday as a result of the first strike by NHS staff in England over pay for 32 years.

The four-hour stoppage, a protest after an expected 1% pay rise was blocked, is intended to force the health secretary, Jeremy Hunt, to make more money available for staff who claim their earnings have been cut by 15% in real terms under the coalition.

But the action by nurses, midwives and other staff comes amid warnings that it will “distress and inconvenience” patients and cause problems for important NHS services.

The five unions whose members will be striking claim Hunt has betrayed them and left them feeling undervalued and undermined, while representatives of hospitals and other important services say the strike has a dubious mandate because few staff voted for it.

Ambulance services are likely to be affected most. About 130 military personnel will drive ambulances in London and the north-west to replace striking drivers. In London an expected shortage of crews has led the capital’s ambulance service to warn that patients with a broken limb or trouble breathing, or who have been involved in a minor road accident, and women in labour may have to make their own way to hospital.

Jason Killens, the London Ambulance Service’s director of operations, said it expected to be “under significant pressure” on Monday as many staff were expected out on strike. “We have plans in place to ensure we reach the most seriously ill and injured patients as quickly as possibleThese include all clinical managers working on the front line, the use of more private ambulance crews and support from other emergency services,” said Killens. “However, people who need an ambulance response, but are not in a life-threatening situation, should expect to wait longer or may not get an ambulance at all,” he added.

The impact of the strike will vary across England. But some hospital trusts expect that it will lead to planned, non-urgent operations, including some surgically assisted caesarean births, being postponed. Pregnant women are likely to face delays to their 12 or 20-week scans. However, trusts hope to minimise disruption and patients’ concerns by doing the procedures later on Monday or within days of the scheduled date.

Jon Skewes, director for policy, employment relations and communications at the Royal College of Midwives (RCM) – whose members will walk out for the first time in its 133-year history – said midwives would continue to care for women and babies and prioritise patient safety during the walkout.

Skewes accused Hunt of not trying to broker a deal. “We have asked him to meet all the health unions but he has chosen not to. That’s an abrogation of leadership by Jeremy Hunt,” he said.

Rachael Maskell, head of health at the union Unite, added: “Hunt is acting totally irresponsibly in not sitting down to try and settle this dispute. It is time he was sacked for his politicking and failing management of NHS staff.”

The NHS Confederation stepped up the pressure on the unions by casting doubt on the legitimacy of the strike, which will be followed by a four-day work-to-rule for the rest of the week, which NHS managers expect will bring further disruption.

“Only around 4% of more than one million NHS staff voted to take strike action on Monday. We hope many will make the right choice for patients and not participate in any industrial action”, said Rob Webster, its chief executive. NHS care providers are “pulling out all the stops to minimise disruption”, he added.

Its breakdown of members who backed strike action in recent ballots held by the unions joining the walkout shows that 46,128 endorsed it, out of a total non-medical workforce of almost one million. Only 26,126 members of Unison – which has 300,000 members in the NHS – did so, as did only 7,032 members of Unite, which represents about 100,000 NHS workers. The unions involved represent less than half the 1 million staff. Others, including the Royal College of Nursing and British Medical Association, which speaks for most doctors, did not ballot.

The Hospital Consultants and Specialists Association, which represents 2,600 senior hospital doctors, said it had advised them not to undertake extra work this week intended to tackle the waiting-list – which Hunt regards as a priority and recently allocated extra funding to pay for a blitz – as part of its compliance with the work-to-rule.

“Hospitals often ask consultants if they can squeeze in an extra theatre list or an extra clinic, to help keep the waiting list as low as they can. But we are asking our members not to undertake any waiting-list initiative work from Tuesday to Friday. That could lead to certain operations being postponed, which could mean waiting lists are extended”, said Eddie Saville, the union’s general secretary.Unite’s Maskell said the pay of the 7,800 senior NHS managers earning at least £100,000 should be tackled to help rein in unacceptable “growing pay inequality” in the NHS. “Forty thousand staff in the NHS are paid less than the living wage, and many now revert to in-work benefits and foodbanks for bare essentials.” Yet, for example, she added, Yorkshire Ambulance Trust executives recently received a 30% pay increase.

Hunt had said the NHS could not afford to give all staff the recommended 1% and that doing so hit patients as that would cost jobs equivalent to those of 14,000 nurses.He also insists that the NHS, whose £113bn budget is under pressure from an ever-rising demand for care, could not afford the 1% while also meeting the cost of annual pay increments, which half of all staff get for extra duties and length of service. Hunt stresses that everyone will receive “at least 1% additional pay” both this year and next year, either by receiving a rise or their usual increment.

Unions, though, point out that the 1% rises that about half of staff will receive will be one-off additions to their salaries and will not be consolidated into them. “We are disappointed that trade unions are taking industrial action and have rejected our proposals to give NHS staff at least 1% additional pay this year and at least a further 1% next year”, said a Department of Health spokeswoman.

“NHS staff are our greatest asset, and we’ve increased the NHS budget to pay for over 12,500 more clinical staff since 2010. We cannot afford a pay rise in addition to increments – which disproportionately reward the highest earners – without risking frontline jobs.”