The NHS’s most senior doctor claims the planned escalated junior doctor strike will “irreparably damage” trust in the profession.

Sir Bruce Keogh, the medical director of NHS England, said the decision to include emergency cover in the strike, planned for 20 hours between 8am and 5pm on April 26 and 27, was a "watershed moment" for the NHS.

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Writing in the Observer he said: “I worry that the withdrawal of emergency cover will put our sickest, most vulnerable patients at greater risk.

“This challenges the ethical framework on which our profession is founded and runs against the grain of our NHS and our personal and professional values.

“Doctors are the most trusted profession. This trust is a privileged gift bestowed on us by society, but it brings responsibilities and expectations.

“One of these expectations is that we are there when people need us most. By withdrawing emergency cover, we risk crossing a line, which will irreparably damage this trust and the reputation of our profession.

“So I encourage every doctor considering withdrawing emergency cover to dig deep and ask whether such action is fair to patients or compatible with the values and privilege of being a doctor.”

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The British Medical Association (BMA), the union doctor’s union, announced the escalated strike action last month after the government's "continued refusal" to re-enter talks on controversial contracts.

The strike will be the third since Health Secretary Jeremy Hunt announced he would impose new contract by August and claimed the union had refused “point blank to discuss reforms”.

Under the contracts junior doctors will get an increase in their basic pay, but will have to work more weekends. Guaranteed pay rises linked to time in the job will be axed and bonus pay for working unsociable hours will be curbed.

The BMA has repeatedly claimed that the contracts imposed by the department of health are "unsafe" and would cause them to be overworked.

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Dr Johann Malawana, BMA junior doctor committee chair, said: "No junior doctor wants to take this action but the government has left us with no choice.

"In refusing to lift imposition and listen to junior doctors’ outstanding concerns, the government will bear direct responsibility for the first full walkout of doctors in this country.

"The government is refusing to get back around the table and is ploughing ahead with plans to impose a contract junior doctors have no confidence in and have roundly rejected."