London’s position as the biggest commercial and specialty underwriting hub is at risk should the UK vote to leave the European Union, a senior Lloyd’s executive warns.

EU membership gives unparalleled advantages to the market, including direct access to Europe’s more than 500 million consumers, and facilitates trade with non-EU countries.

The London market accounts for more than £60 billion ($123 billion) of gross written premium, and at least £6 billion ($12 billion) of premium income comes from the EU.

“These benefits are, in my view, critical to the success of the London insurance market and its position as the world’s largest specialist insurance and reinsurance centre,” Lloyd’s Chief Risk Officer and General Counsel Sean McGovern said.

“It may be a statement of the obvious, but exiting the EU will create a level of uncertainty for Lloyd’s, for the London market, as well as the UK and European economies, that we have rarely experienced.”

UK Prime Minster David Cameron hopes to secure a membership reform package when the EU meets in Brussels this week, before putting it to a referendum.

Lloyd’s is leaving nothing to chance, and has started making contingency plans for a number of possible scenarios, including “Brexit” – a British exit from the union.

“The objective [is] to ensure Lloyd’s can continue to provide our market with access to the EU,” Mr McGovern said. “While there will be more work to do in the event of a vote to leave, we are confident this objective can be achieved and we will… provide ways to allow business to continue to be written on both a cross-border and a branch basis.”