Updated

The president of one Britain's biggest business lobby groups is to warn of the devastating consequences of the country leaving the European Union without having secured a wide-ranging trade deal.

In prepared remarks for a speech due later Thursday, Paul Drechsler will say that a "'no deal' scenario would open a Pandora's Box of economic consequences."

If Britain ends up leaving the EU without a deal, it would have to rely on so-called World Trade Organization rules.

For Drechsler, this "worst-case scenario" would hurt firms on both sides.

Britain, he added, would face tariffs on 90 percent of its EU exports by value and a raft of new regulatory hurdles. As a member of the 28-country bloc, British firms don't have to pay any tariffs to trade in the EU.