The leading voice in Britain's pharmaceutical industry has warned the sector is at a "critical juncture" as it hopes for a Brexit deal that can unify regulations between the UK and Europe.
Lisa Anson, president of the Association of the British Pharmaceutical Industry (ABPI), told Sky News that firms have put investment decisions "on ice" and face a "dire situation" unless such an agreement can be reached.
The industry has welcomed the progress in Brexit negotiations announced at the end of last week, but remains deeply concerned about a number of issues, particularly the ways in which medicines would be distributed around Europe after Brexit.
Ms Anson said there were clear priorities for her sector, which employs around 73,000 people in the UK .
These were access to skilled staff, a clear set of regulations to support the safety of patients and links to the NHS that means patients get the same access to medicines as they do in other countries.
"The bottom line is the issues are understood - we're all agreed on the issues - what we need is urgent progress into tangible action," Ms Anson said.
"As companies, we are already driving contingencies because we have to make sure we have the ability to supply medicines.
"Every month 45 million packs of medicine go from the UK into Europe, 37 million packs come back the other way.
"And every pack is a patient needing a medicine, from babies having their vaccinations to people with chronic disease like diabetes, even patients awaiting a surgery, wanting their anesthetic.
"Every single one of those patients depends on us having the supply chain for medicines, which is complex and scaled, in place.
"And we simply can't afford to wait so we're having to take action now to make sure we're in a position because we don't have certainty about some of the outcomes."
To that end, Ms Anson revealed that her own company had already prepared plans to deal with disruption to trade.
She (Munich: SOQ.MU - news) said: "If we look at the frictionless trade, AstraZeneca is already looking at contingencies to duplicate the quality control release processes in the UK and in Europe, because we can't afford to wait to know if there's going to be customs tariffs or any other sort of barrier.
"We need to know that we can supply the medicines within Europe."
She said the pharmaceutical sector had a particular nervousness about retaining skilled staff, with around 25% of the workforce coming from abroad:
"It's absolutely essential in a globally competitive world that we have the scientific talent that we need to drive a world-class life sciences sector in this country.
"It is fair to say that people are already turning down jobs in the UK - we've seen that in our own company."
"If you think about investment decisions right now, I think it would be fair to say, if you look at manufacturing in particular, those are on ice.
"Because we simply don't know how we're going to continue the supply chain of medicines or what terms we're going to be operating under."
It is a picture of nervousness, of an industry worth many billions to the British economy, but unsure of what happens next.
There is no more regulated industry than pharmaceuticals, none that is so reliant on sticking to rules and requirements.
Few sectors need such a high level of international co-operation.
Take UCB, a Belgian pharmaceutical company with a substantial presence in Britain.
In its factory in Slough, I met Neil Weir, the company's Head of Discovery Research, who combines traces of optimism and anxiety.
He said: "The pharmaceutical sector operates within highly integrated regulatory systems and supply chains, so we hope that a 'hard Brexit' can be avoided and on-going close regulatory co-operation between the UK and the EU can be achieved to enable us to supply patients with the medicines they need without disruption."
"We hope we will get clarity on these issues.
"However, as an organisation with UK based research and development, we do believe that full implementation of the recent life sciences industrial strategy by Government can enhance UK's position as an attractive destination for R&D [research and development]."