LONDON (Reuters) - The British government sought to reassure drug companies and biotech firms on Monday by calling for continued co-operation with the European Union over drug regulation after Brexit.

Flags are arranged at the EU headquarters as Britain and the EU launch Brexit talks in Brussels, June 19, 2017. REUTERS/Francois Lenoir

Drugmakers, which overwhelmingly favored remaining in the EU, account for 25 percent of all UK business research spending and companies have warned that Brexit threatens uncertainty, added complexity and potential drug approval delays.

Jeremy Hunt, the health minister, and Greg Clark, the business minister, wrote a letter to the Financial Times outlining how Britain and the EU could work together.

The letter said the government’s priority was to protect patient safety, maintain Britain’s role as a center for research and promote public health globally.

The ministers said there were numerous examples where the partnership between Britain and the EU had helped patients, including the licensing of 130 products for rare diseases.

“We will look to continue to work closely with the European Medicines Agency (EMA),” they said.

“Our overall aim is to ensure that patients in the UK and across the EU continue to be able to access the best and most innovative medicines.”

The London-based EMA currently acts as a one-stop-shop for approving and monitoring the safety of drugs across the EU, but Britain is expected to leave its oversight after Brexit. The agency itself is due to relocate to another city inside the EU.

In a bid to limit disruption, drugmakers have been pushing for some kind of partnership deal with the EMA after Brexit, potentially allowing for mutual recognition of medicine approvals.

EMA Executive Director Guido Rasi said in April this kind of arrangement was theoretically possible but it would be up to EU governments to decide whether to offer such a deal, since Britain will be outside the single market governing free movement of goods, capital, services and people.

Being isolated from the EU system could put British patients at the back of the line for new drugs if companies decide to prioritize Europe, a market of 500 million people, over the UK, where commercial opportunities are far smaller.

Shire SHP.L CEO Flemming Ornskov said on Monday that the future of the EMA was his principal Brexit concern.

“What is going to happen with the European Medicines Agency? I have 20 projects in late-stage clinical development, so clarity is important,” he told Reuters in an interview.

Although the impact of Brexit on global companies like GlaxoSmithKline GSK.L and AstraZeneca AZN.L is likely to be limited, the UK pharmaceuticals trade association has warned that having Britain outside the EU could undermine future investment, research and jobs in the country.

Mike Thompson, CEO of the Association of the British Pharmaceutical Industry, said the ministers’ letter was “a welcome recognition that the future of medicines regulation is a key priority for the government”.