Jeremy Corbyn has claimed official documents obtained by the Labour party show that the US is demanding the NHS will be “on the table” in talks on a post-Brexit trade deal.

The Labour leader said the uncensored papers gave the lie to Boris Johnson’s claims that the NHS would not be part of any trade talks and revealed that the US wanted “total market access” after the UK leaves the EU.

What has Boris Johnson said?

Johnson has repeatedly denied that the NHS is on the table in any trade talks or for sale. On 25 July in the House of Commons, the day after he was appointed prime minister, he told MPs: “I will make one important point that it is worth making: under no circumstances will we agree to any free-trade deal that puts the NHS on the table. It is not for sale.”

He has repeated that position during the election campaign, including on 19 November in the ITV leadership debate. “There are no circumstances … in which this government or any Conservative will put the NHS on the table in any free-trade negotiation,” he said.

After the publication of the unredacted record of trade talks between the UK and US, he maintained the line while campaigning in Cornwall on Wednesday. “The NHS is not on the table in any way,” Johnson said.

What do the documents show?

The documents show that between July 2017 and July this year, trade talks between the UK and US have covered the NHS, drug pricing and patents, the pharmaceutical industry and medical devices, in the context of the future trade landscape between the two countries.

US trade officials explained clearly their approach to trade talks, described as “negative listing”, which involves starting the talks with nothing off the table, the assumption being that total market access is the starting point for any discussions.

Play Video 3:10 Jeremy Corbyn reveals 451-page unredacted document 'proving NHS up for sale' – video

How does drug pricing in the UK work now?

The UK has some of the lowest drug prices in Europe. A key reason for that is the existence of the National Institute of Health and Care Excellence (Nice), which Tony Blair’s Labour government set up in 1999. It is an independent expert body that assesses evidence and issues guidance to the NHS and health professionals about which drugs, types of surgery and other forms of treatment benefit patients and are worth spending money on. As such it determines what drugs do and do not represent value for money for NHS bodies in England and Wales to buy to give to patients.

Nice has a ceiling of £30,000 per year of “good quality life” gained, rising to £50,000 for end-of-life drugs such as cancer drugs. Nice’s judgments help keep prices down by capping what the NHS can spend on them. So does the NHS’s status as a bulk buyer of drugs, and EU-wide rules on patents.

What do the Americans want to change?

The minutes of the trade talks show the Trump administration and US pharmaceutical interests want the British government to dismantle the safeguards that protect the NHS from paying high prices for drugs. (Drugs in America cost two and a half times what they cost in the UK.)

They want, for example, “full market access” for US drugs, which would greatly limit Nice’s ability to decide which medicines patients can receive. They also want future prices to be “market-derived” or “competitive”, which again would lead to Nice being marginalised.

Corbyn mentioned patents. Why do they matter?

Crucially, US officials want longer patents for American drugs, which would boost their makers’ profits and limit the NHS’s scope to buy much cheaper generic versions. They have suggested in the talks a number of changes, all of which – if agreed – would benefit pharma firms financially. They include “patent linkage”, grace periods and “patent term extension and adjustment”, which UK officials described as “the three big defensive areas for us” in detailed discussions about drug patents.

This is a difficult issue for the UK because it is a leading member of the European Patent Convention, though it is not an EU body.