Howard Kingsnorth via Getty Images Britain's exit from the European Union leaves questions about what will happen to the pharmaceutical industry during the transition period.

British patients could lose access to vital medicines unless arrangements are put in place to ensure a seamless licensing system after Britain leaves the European Union, a top industry official said on Wednesday.

There are more than 5,000 medicines approved through the current regulatory process and manufacturers will need an appropriate product license to still make them available in Britain once ties with the EU are broken.

“It’s in all of our interests to make sure that, from day one, those medicines are there and available,” Virginia Acha, executive director of research at the Association of the British Pharmaceutical Industry, told a parliamentary committee.

“Otherwise, the real penalty will be paid by the lady in Strathclyde or the gentleman in Hove who can’t get the medicine they need and rely on for their health. That’s just not something we can play around with.”

The post-Brexit status of prescription drugs will depend on whether Britain requires UK-specific licenses on day one or whether there is a transition period for transferring current product licenses to a new system.

Britain faces a two-year countdown to exit once the government gives formal notice of its intention to leave the EU, as Prime Minister Theresa May has pledged to do by March 2017.

But there is a growing discussion about possible transition arrangements to avoid a “cliff edge”, which would be damaging for businesses across a range of industries. May hinted last week she might be open to such a transitional deal.

The highly regulated nature of pharmaceuticals makes regulatory oversight a top concern for drugmakers, who currently use the European Medicines Agency (EMA) as a one-stop-shop to get drugs licensed across Europe.

The EMA is based in London for now but it is likely to move to another city within the EU after Britain leaves the bloc.

Leading drugmakers, including GlaxoSmithKline and AstraZeneca, opposed Brexit in the run-up the June 23 referendum and the industry is pushing hard to keep Britain within the European regulatory network in some way.