More than 500 NHS doctors, nurses and other workers have written to Donald Trump to ask him to take the health service off the table during UK-US trade talks.

In a letter sent to the US president as he travelled to the UK, the medics asked him to “rule out once and for all any increases to the cost of US drugs for our NHS and any trade deals that include NHS contracts”.

Internal UK government documents published by Labour last week revealed that the US was pushing for longer drug patents and for UK public services to be opened up to American companies after Brexit.

Mr Trump arrived in London on Monday night ahead of a two-day Nato summit.

He is expected to face questions about the role of the NHS in trade talks, with the Conservatives desperate for him not to say anything that could fuel public concerns that Boris Johnson may agree to the US demands.

The Tories have insisted that the NHS will not be part of any trade talks and Mr Johnson has said he would walk away if Mr Trump made the issue a red line.

In their letter to the US president, however, the NHS workers wrote: “We are alarmed to read about documents revealed on Tuesday that showed the US government have been in secret talks with our government about the opening up of British markets after Brexit and what this could mean for the future of our National Health Service.

“We are particularly concerned about the conversations over patents for pharmaceutical products and the potential for huge drug price increases for the NHS and the rest of the world.”

The medics said Mr Trump had claimed earlier this year that the NHS would not be on the table during trade talks but that he had since rowed back on this.

They wrote: “This week we would like you to rule out once and for all any increases to the cost of US drugs for our NHS and any trade deals that include NHS contracts. We want the NHS off the table completely.

“However words on their own are not enough. To allay our worst fears, we request that you publish new trade negotiating objectives that explicitly rule out any measures that will lead to changes to our pharmaceutical patent and procurement regime, explicitly state that the NHS is ‘negative listed’ and taken off the negotiating table in a US-UK trade negotiation, and a commitment that trade talks will no longer be held in secret.

“Anything less than this will not reassure us and will leave thousands of dedicated NHS staff in fear for the future. The NHS is our most treasured institution and we will fight to defend it.”

NHS workers are expected to lead a protest organised by the Stop Trump Coalition during the US president’s visit.

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In a separate letter sent ahead of the Nato summit, Jeremy Corbyn called on Mr Johnson to halt trade talks until Mr Trump has amended the US’s negotiating position.

The Labour leader urged the prime minister to ensure that the US agree that pharmaceuticals will not be part of any deal, that UK health spending watchdog Nice will continue to determine the cost-effectiveness of drugs, and that American companies will not be given access to UK public services after Brexit.

Mr Corbyn wrote: “The threat to the NHS from a future post-Brexit US-UK trade agreement, given the statements made by both US and British officials and politicians, is of profound concern to the British public.”

He told Mr Johnson: “While you have claimed that NHS medicines procurement is ‘not on the table’ in UK-US trade talks, that claim has now been shown to be false. The evidence is clear that you have misled the public ... President Donald Trump and his administration have made no secret of the fact that they intend to use a future trade deal with the UK to drive up the cost at which the NHS buys drugs.”

Arguing that “full transparency about the threat to the future of our NHS is vital” ahead of the 12 December general election, he added: “The public need to know that all aspects of our health service are genuinely off the table in any UK-US trade talks, and that no part of the NHS or our health system will be up for sale.”

Boris Johnson reminds Donald Trump not to interfere with general election

Boris Johnson reminds Donald Trump not to interfere with general election

The documents released by Labour last week revealed that the US wanted to make “total market access” to UK services “the baseline assumption of the trade negotiations” and believed that “everything in services should be open unless there was a very good reason not to”.

The memos also said that the US had “pushed hard” for longer drug patents after Brexit – a move that would likely drive up the price of drugs in the UK.

The Conservatives have repeatedly insisted that the NHS will not be part of any trade deal.