A former Conservative health secretary has agreed the NHS is under threat from a trade deal with the US after Brexit, warning: “We have to resist them.”

Andrew Lansley joined critics of Donald Trump’s call for the health service to be “on the table”, predicting a demand to open it up to giant US firms – ramping up the price of medicines in this country.

“It is quite clear that what they will actually target is the process by which we control pharmaceutical pricing,” Lord Lansley said.

“That is where they will be pushing. We have to resist them – otherwise there will be serious budget consequences.”

Conservative leadership contenders have dismissed the risk posed by the US president’s comments, most insisting the NHS will not be “up for sale”.

But Lord Lansley’s intervention highlights how experts agree the real danger is not to services – which must, controversially, already be offered to private firms, after changes introduced under David Cameron.

Instead, US negotiators have already said they will demand an end to NHS controls on medicine costs in favour of US-style direct-marketing of drugs.

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Lord Lansley said Washington would seek to end the system where the National Institute for Clinical Excellence (NICE) negotiates discounts and rules some drugs are too costly.

He pointed out legislation had been passed in the US against such a system, adding: “The Americans don’t like this.

“They want prices to be controlled in a market context – whereas the NHS is a single buyer and the government has the power to control prices.”

Dr Sarah Wollaston, the former GP and now Independent Group MP, agreed the threat was real, not least because the UK, if Brexit goes ahead, would be going “cap in hand” for a deal with the US.

She pointed out that the NHS’ drugs bill had already soared from £4.2bn in 2010 to £9.2bn last year, even while it had a “strong hand in negotiating the best possible price”.

“This is a very serious issue,” Ms Wollaston warned, “if those kinds of deals are scrapped, the implications for costs for the NHS would be extraordinary.

“If we are in a position where we are having to go cap in hand to the US for a trade deal, there is a risk they would use that muscle.”

Ms Wollaston called for all the leadership contenders to “explicitly say drug pricing will not be on the table”.

Many had been quick to react to Mr Trump’s incendiary comments, but without referring directly to issue of dug prices.

Matt Hancock, the health secretary, tweeted: “Dear Mr President. The NHS isn't on the table in trade talks - and never will be. Not on my watch.”

He was swiftly followed by both no-deal hardliner Dominic Raab and pro-Final Say referendum Sam Gyimah.

The US has pressed for demanding liberalisation of drug pricing in previous trade negotiations with Australia and New Zealand, only to back away.

However, some experts believe that – because of the NHS’s global significance and market power – Washington will push the UK harder, if Brexit goes ahead.