Labour says it has evidence the NHS would be at risk under a post-Brexit trade deal with the US.

At a press conference in London, Labour leader Jeremy Corbyn said he had a 451-page dossier showing initial talks had taken place on drug prices and the NHS.

He warned it showed the future of the health service was at risk.

But Prime Minister Boris Johnson said the claims were "total nonsense" and he could give a "cast-iron guarantee" the NHS would not be part of formal talks.

In the Conservative manifesto, published at the weekend, the party explicitly stated neither the price paid for drugs nor the services provided would be "on the table".

But Labour has now released uncensored government documents covering six rounds of negotiations - preparatory meetings ahead of formal trade talks - in Washington and London between July 2017 and July 2019.

These documents appear to provide more detail about the meetings Channel 4's Dispatches programme reported on earlier this year.

And they show the US is interested in discussing drug pricing - mainly, extending patents that stop cheaper generic medicines being used.

The US currently pays two and a half times more for drugs than the NHS does.

As well as the pharmaceutical industry, the talks covered agriculture and climate change.

One document quotes a UK official saying the talks are helpful in determining the areas the US may want to discuss, while acknowledging the UK would have objections.

Idea of NHS being up for sale will be furiously disputed

This is going to be furiously disputed throughout the day.

Jeremy Corbyn doesn't provide evidence ministers have agreed the health service should be part of a trade deal with US.

But details of discussions about the demands of US pharmaceutical companies will still be motivating for Labour voters worried about the NHS.

"Not for sale," has been the biggest mantra at Labour events, even though the Tories have always furiously denied the NHS is in any way "up for sale".

It's clear US drug companies want access to UK markets - Labour suggests the UK has agreed they could extend the patents on some medicines, which could cost the NHS more, for example.

But whether any UK government would ever do a deal that made medicines much more expensive for the NHS, and therefore the taxpayer, which would be massively costly for the government and probably prove deeply unpopular, is a big political question.

Mr Corbyn said the documents showed talks were at a "very advanced stage" and gave the lie to Boris Johnson's claims the NHS would not be part of any trade talks.

"The uncensored documents leave Boris Johnson's denials in absolute tatters," he told a news conference in London.

"We have now got evidence that under Boris Johnson the NHS is on the table and will be up for sale.

"He tried to cover it up in a secret agenda and today it has been exposed."

The claim the NHS would form part of a free-trade deal with the US under the Tories has been one of the Labour's key attack lines in the general election campaign.

Reacting to Mr Corbyn's latest claims, International Development Secretary Liz Truss said it was simply a stunt.

"Jeremy Corbyn is getting desperate and is out and out lying about what the documents contain.

"People should not believe what he says."

Mr Johnson, meanwhile, said the claims were "total nonsense".

"This is continually brought up by the Labour Party as a diversionary tactic from the difficulties they are encountering," he said.

And he could give an "absolute cast iron guarantee" the NHS would not be on the table.