NICOLA Sturgeon has intervened in the junior doctors’ strike in England, calling on David Cameron to get back around the negotiating table and expressing concerns of the “knock-on effect” on NHS Scotland.

For the first time in the health service's history, it has experienced its first all-out strike, affecting emergency cover with more than 125,000 appointments and operations cancelled.

More than 20,000 junior doctors are thought to have been on strike with further industrial action continuing today.

The First Minister has written to Mr Cameron expressing “increasing concerns” about the strike's knock-on effect in Scotland while her predecessor Alex Salmond joined a picket at St Thomas' Hospital in Westminster.

Ms Sturgeon made her intervention following a request for support from the presidents of the three Scottish-based royal colleges after they raised concerns that the imposition of the contract on junior doctors in England would “have far-reaching and unintended consequences for healthcare across all nations in the UK for the foreseeable future”.

She said: “The NHS in England and relations between the UK Government and the NHS workforce are not a direct matter for me but the longer this strike continues the more concerned I have become about a knock-on effect on the profession across the whole of the UK.”

In her letter to Mr Cameron, she noted that while the NHS was devolved, there was “considerable cross-over between medical schools, training of junior doctors and the development of professional skills by the royal colleges between Scotland, England, Wales and Northern Ireland.”

The FM went on: “To alienate or drive away this group of doctors from the profession risks the skills and resources that would be available across the UK in the future and the on-going dispute and apparent refusal of your government to return to negotiations risks the reputation of the UK as an employer internationally.”

Ms Sturgeon added: “Given my increasing concerns about the spill-over effect of the current impasse and the message it sends across the world over the support of the medical profession in the UK, I would urge you to reconsider the current position and to return to the negotiations with the BMA.”

No 10 said Mr Cameron would reply in due course.

Across England, hospitals appeared to have coped well with low waiting times across A&E departments and no urgent calls for doctors to return from the picket lines.

Oliver Warren, a consultant surgeon at the Chelsea and Westminster Hospital NHS Foundation Trust, tweeted: "Update from frontline - all going well! 3 consultant ward round, all pts (patients) seen - morale high. Off to ED to review a pt."

Earlier, Jeremy Hunt, the Health Secretary south of the border, made clear the UK Government would not be "blackmailed" into dropping its election manifesto pledge for a seven-day health service.

But the junior doctors argue the proposed changes will mean cuts to pay, especially for work during evenings and weekends as well as long working hours, which, they argue, will compromise the safety of both doctors and their patients.

As the strike began, the Prime Minister denounced it, stressing how he was backing Mr Hunt’s handling of the dispute.

"There is a good contract on the table with a 13.5 per cent increase in basic pay; 75 per cent of doctors will be better off with this contract,” he declared.

Mr Cameron added: "It's the wrong thing to do to go ahead with this strike and particularly to go ahead with the withdrawal of emergency care; that is not right."

Meantime, Labour leader Jeremy Corbyn joined thousands of junior doctors as they marched through Whitehall following a day of strikes.

Leading the march from St Thomas' Hospital and flanked by John McDonnell, the shadow chancellor, he said: "The Government has an opportunity to settle this, they should get on and do so."

SNP MP Alex Salmond, the former First Minister, was also pictured at an NHS picket line in London.

Elsewhere, author JK Rowling, who is married to a doctor, tweeted support for the strikers, saying: "Doctors who have been loyal 2 the NHS for years rather than chase £ abroad don't deserve to be accused of greed."