UK health secretary Steve Barclay on Wednesday doubled down on the government’s decision not to negotiate on pay with striking NHS staff, as he accused ambulance unions of jeopardising patient safety.

Barclay accused the unions of making a “conscious choice to inflict harm on patients” and criticised them for failing to provide sufficient cover of 999 calls. “Not all category two calls are being covered by the unions . . . they are being triaged,” he told the BBC’s Today programme.

Unions reacted furiously to the health secretary’s comments. Sharon Graham, general secretary of Unite, said: “To say that ambulance unions have taken a conscious choice to inflict harm on patients is a blatant lie.”

Rachel Harrison, national secretary of the GMB union, insisted that ambulance workers were “seething at such a crude, insulting attempt to divert attention from the government’s continued chaos in the NHS”.

The government is braced for severe disruption within the NHS across England and Wales, following the decision by about 10,000 ambulance workers represented by the Unison, GMB and Unite trade unions to walk out over pay and working conditions.

Most ambulance services are set to respond to life-threatening “category one” calls, as well as serious “category two” emergencies. The public have been urged by the NHS to only call 999 in a “medical or mental health emergency” and urged by ministers not to engage in “risky” activities.

The health secretary reiterated the government’s decision to accept the guidance of the independent pay body, which had recommended 1mn NHS workers on Agenda for Change contracts receive a pay rise of £1,400 backdated to April.

He added that next year’s pay review process was already under way. “Obviously that body will then consider the changes in inflation, the other issues that have been raised,” he said.

Meanwhile, the Royal College of Nurses has “overwhelmingly” rejected the Scottish government’s pay offer, which would have resulted in an average increase of 7.5 per cent. The union will announce dates for industrial action in the new year.

The Association of Ambulance Chief Executives, an organisation that supports ambulance services in England, has urged both the government and unions to “do everything in their power to find resolutions”. However, the rhetoric showed no sign of cooling on Wednesday as ambulance unions forcefully rejected Barclay’s suggestion that their strikes put patient safety at risk.

NHS bosses have continued to voice alarm over the mounting pressures facing the health service, with eight ambulance services this week declaring critical incidents, a status triggered when services are at risk of being overwhelmed by patients.

Matthew Taylor, chief executive of the NHS Confederation, warned that the health service could not “afford to drift into a winter of industrial action”, as he urged unions to work to “minimise patient harm” during today’s strikes.

“In most parts of the country the ambulance service is well away from meeting its targets for responses to those kind of category two cases,” he told BBC Breakfast. “So, this strike could not be happening at a worse time,” Taylor added.