Britain’s decision to leave the European Union may have adverse implications for the UK insurance industry, Fitch Ratings warns.

“The international nature of much of the business placed through Lloyd’s of London insurers could increase downgrade risk if economic uncertainty leads to a material portion of international policyholders placing their business overseas,” the ratings agency says.

Fitch says reduced co-operation between UK and EU regulators may put a limited number of holding companies at risk of downgrade.

But any impact from a weaker exchange rate should be manageable and temporary, and UK non-life insurers are less sensitive to asset value deterioration than life insurers.

Lloyd’s CEO Inga Beale said in a letter to the Financial Times last week that London can maintain its position as the global heart of specialist insurance and reinsurance following Brexit, but negotiations should move as swiftly as possible towards a satisfactory result.

“The Government must start the withdrawal negotiations now, and with authority,” she wrote. “MPs are elected into public office to lead. Now they must do so.”

Former head of the British civil service Andrew Turnbull told a Treasury select committee that leaving the EU may help the insurance industry if it also puts the sector outside the Solvency II regulatory framework, according to the London Telegraph.

Lord Turnbull says Solvency II makes life difficult for companies that want to expand into Asia and the US.

“A European-based and regulated insurance company is at a disadvantage relative to a Canadian or American one,” he said.

Stephen Netherway, the head of law firm CMS’ financial institutions insurance group in London, says the referendum result is “seismic” for the global insurance market based in Britain.

“The playbook for distribution and route to European market has just been ripped up, and we enter the world of [Donald] Rumsfeld’s unknown unknowns,” he says.

“For non-EU-domiciled insurers and brokers based here, first up for review must be ‘redomicilisation’ to preserve the certainty of single-market access.”

Mr Netherway says in an article on the Irish website Lawyer.ie that questions raised by the vote include whether Dublin could become a new EU base for many UK financial institutions.