Demands have been made for an official inquiry into claims Department of Health staff encouraged an NHS boss to harden the language of a letter raising concerns about a strike by junior doctors.

Sir Bruce Keogh's letter raised fears about whether striking junior doctors would be available to respond in the event of a Paris-style terrorist attack.

Emails reveal the letter went through a number of revisions to ensure concerns about the possible impact of a major incident during the walkout were made as "hard-edged" as possible, according to the Independent.

Health Secretary Jeremy Hunt was also given approval of the text, emails between the Department of Health (DoH) and the national medical director of NHS England reveal.

Liberal Democrat health spokesman Norman Lamb has called for a Cabinet Office inquiry into the reports, which he said raised "serious concerns about potential political interference" which could damage trust between the Government and junior doctors still further.

And Lib Dem leader Tim Farron called for Mr Hunt and Sir Bruce to be summoned before the House of Commons Health Committee to answer questions about the letter.

"The Government have poisoned the well of relations between junior doctors and NHS bosses," said Mr Farron.

"Tory ministers said when they set up NHS England it would be free of interference. These words have been shown to be meaningless. The Tories are guilty of blatant and utter hypocrisy over this sorry saga."

Talks between the Government and the British Medical Association (BMA) aimed at resolving a dispute over a new contract for junior doctors are resuming ahead of three spells of strike action.

In an email sent the day before the first strike was declared, a DoH official told Sir Bruce the risk of a "major incident" would be "pressed quite hard in the media once the strike is formally announced" and he was advised that "the more hard-edged you can be on this, the better", according to the newspaper

Mr Hunt agreed Sir Bruce would not be asked to speak to the media on the day the strike was declared "so long as" his letter underlined his opposition to the walkout, it added.

Asked to confirm he was "happy" with changes, an official told the health service chief: "I am sure then that JH [Jeremy Hunt] will be interested to see the proposed final product; my hope is that if you are happy to make these changes we will be able to get him over the line."

The department said it was "absolutely right" that ministers insisted on Sir Bruce giving his "independent" view on how the health service would be able to respond.

Mr Lamb said: "We need a cross-party commission to look at how we secure the long term future of the NHS and social care, but Jeremy Hunt must now immediately get back around the negotiating table and resolve this dispute with junior doctors that are such an integral part of our NHS."

A Department of Health spokesman said: "Industrial action of the kind planned by the BMA creates a major safety risk for patients so it was absolutely right that ministers insisted on Sir Bruce Keogh giving his independent view of the NHS's capacity to respond in the event of a major terrorist incident."