NHS bosses fear hospitals and patients will have to pay billions more for drugs as the price of Boris Johnson striking a post-Brexit trade deal with Donald Trump.

A report by the NHS Confederation, which represents most hospital trusts in England, warns that the NHS could be landed with a much larger bill for medication and denied the chance to use cheaper alternatives to expensive branded drugs.

The voluntary pricing and access scheme (VPAS), which caps the total bill the NHS has to pay for medicines, would be under threat, given the determination of the US government and drug companies to force Britain to pay higher prices, it says.

“Regarding pricing, the USA objectives [in the trade deal talks] seek to ‘provide full market access [in the UK] for US products’... Under the [VPAS] scheme, NHS expenditure on branded medicines is capped, ensuring predictability of expenditure for the NHS on the entire branded medicines bill.

“One can imagine that such a scheme would not meet the USA’s objectives, which if achieved would result in higher prices for medicines and pass on costs to both patients and the NHS,” the report says.

It comes after a Channel 4 Dispatches documentary revealed that British trade officials have held six official, and five undeclared unofficial, meetings with their American counterparts to discuss drug pricing.

It also cited new research from Dr Andrew Hill, a leading expert on the drugs industry and adviser to the World Health Organisation, that a transatlantic trade treaty could send the NHS’s drugs bill ballooning from £18bn to £45bn a year.

Labour has seized on Dispatches’ disclosures as an early weapon in the general election campaign. The programme has left Johnson and the health secretary, Matt Hancock, struggling to respond effectively to claims that they are selling out the NHS as part of the the planned trade deal.

Trump has made clear that countries must pay more for drugs made by American firms as a pre-condition of agreeing a trade deal with the US.

But NHS leaders want the government to tell the US it will not do anything that would increase the price the NHS pays, or stop it using certain medications. The report says that “the government should consider...maintaining early access for NHS patients to generic medicines by resisting extension of intellectual property rights [and by] resisting provisions that could increase the cost of medicines by changing pricing and reimbursement schemes”.

The latter refers to the arrangement in the VPAS, in which drug firms repay the NHS any sum of money it has paid over and above the amount set in the overall cap for that year.

Jonathan Ashworth, the shadow health secretary, said: “Senior NHS leaders are absolutely right to warn of the dangers of the NHS’s drugs bill skyrocketing as a result of a UK-US trade deal.

“Donald Trump has made it plain he wants to drive down drug prices in the US by forcing other countries to pay more. The price of Boris Johnson’s US trade deal will see the NHS’s drug bill rocketing to £500m a week.”

Trump administration’s view is that any country wishing to conclude a trade deal with the US must agree to pay higher prices for US drugs, so that it can cut the cost of medication domestically, which are the world’s highest.

A government spokesperson said: “The NHS is not, and never will be, for sale to the private sector, whether overseas or domestic‎. The government is committed to the guiding principles of the NHS – that it is universal and free at the point of need.

“The government will continue to ensure that patients have access to clinically and cost-effective medicines that are affordable to the NHS, and that decisions on how to run public services such as the NHS are made by the UK government and the devolved administrations, not our trade partners.

“The sustainability of the NHS is an absolute priority for the government. We could not agree to any proposals on medicines pricing or access that would put NHS finances at risk or reduce clinician and patient choice.”