Unless you suffer from a debilitating illnesses such as Crohn’s disease or rheumatoid arthritis, you are unlikely to have heard of Humira. It’s a revolutionary drug made by the US pharmaceutical company AbbVie that has transformed the lives of thousands of sufferers. It’s also the drug that costs the NHS more than any other – £450m a year.

Humira is a drug that featured prominently in my recent Dispatches investigation for Channel 4, Trump’s Plans for the NHS, which examined how a UK trade deal with the US after Brexit might affect the NHS. It was in this programme that a source with knowledge of the early stages of trade talks told us that discussions had taken place between British and US trade officials that were likely to affect the price the NHS pays for medicines such as Humira. In the UK, the NHS pays around £1,400 per packet for Humira, but it can cost seven times as much in the US.

Our source told us to forget about suggestions that US corporations were going to buy up hospitals, medical services and fleece the NHS – this was just political scaremongering. But they said that the key issue worrying some inside Whitehall was negotiations relating to the complex world of intellectual property (IP) and patent law, which could pave the way for US drug firms demanding higher prices for their medicines and over a longer period of time.

The documents released today by Labour appear to prove that drug pricing has indeed been a subject of initial trade discussions. Our source also told us that not only had these issues been discussed in the formal trade and investment working group meetings, but that there had been five “informal“ meetings at which British trade officials had met US pharmaceutical interests. The documents released today also seem to stand this up. Amid the notes there is an admission that, following the session on intellectual property on 5 November 2018, Department of International Trade officials had “positive bilaterals” and met groups including the US pharmaceutical lobby (PhRma) to discuss priorities for future trade agreements.

We know what PhRma’s priorities are: it has set them out in black and white. It hates the NHS’s position as a near-monopoly purchaser of medicines, which gives it a strong bargaining position to drive prices down. It also wants to end the ability of Nice, which regulates medicines in the UK, to block drugs that it does not consider value for money, and it wants a system more favourable to extending monopoly rights to US drug firms than currently exists in the UK. Its submission to the office of the US trade representative, Robert Lighthizer – the man who will be running the trade talks for President Donald Trump – says the US government should look to recent trade deals with Korea, Mexico and Canada, which has seen the US win concessions on drug pricing.

Dispatches reporter Antony Barnett. Photograph: Pro Co/Channel 4 images

Now none of this means any future British government has to accept the reforms the Americans will ask for. It’s all a negotiation, after all. But while we were filming in the US it became clear that soaring medicine prices across the Atlantic are moving high up the political agenda. Rather than blame the drug firms, Trump claims foreign “freeloaders” are paying too low a price for US medicines. He has publicly told his chief trade negotiator Lighthizer to make drug prices the top priority in any talks with trade partners. In our programme, we interviewed Stephen Vaughn, who until April was Lighthizer’s top legal adviser, and he told us he didn’t know what Boris Johnson meant when he said the NHS was off the table. Vaughn told us that any deal would have to be acceptable to Trump and that if the UK took pharmaceuticals off the table then, we would have to offer up something instead. That is, after all, how trade negotiations work, he explained. As the man who helped to wrangle concessions on drug pricing in recent trade deals with Korea, Mexico and Canada, he knows what he is talking about.

One area where the US succeeded in these deals was over the “high priority” issue of medicines known as biologics. These are cutting-edge drugs made from living organisms such as Humira, and are predicted to become a much larger part of the NHS drugs bill in the future, as they’re used to treat everything from cancer to Alzheimer’s.

Last year, British doctors were allowed to prescribe drugs that do exactly the same job as Humira but at a fraction of the cost. They are known as biosimilars and are the equivalent of generic drugs in relation to chemical drugs. This will save the NHS more than £150m a year, equivalent to the cost of employing thousands of doctors and nurses. In the US, the system of intellectual property and patent law means these cheaper drugs can’t be offered to patients until 2023.

It is the loss of these potentially huge savings that is worrying people like our source, but also senior figures in the NHS. Their concerns may be assuaged by the Conservatives’ statement today, that not only is the NHS not on the table but that “the price the NHS pays for drugs will not be on the table”. Let’s hope that, on this critical matter, ministers will stick to their word or for the NHS it could be a bitter pill to swallow.

• Antony Barnett is a reporter for Channel 4’s Dispatches