Barclays said financial markets had failed to grasp the sheer "breadth" of the British vote, calling it one of "the most significant global risks of the year", and one which could lead to the collapse of the European project.

Investors have been selling off the pound in anticipation of an EU referendum, which could take place as early as the summer. Sterling has depreciated by 9pc against the single currency since November.

But if Britain voted for an EU exit, the political and institutional reverberations on the continent would be far greater than any economic fall-out, said the bank, who compared the implications to that of a "Grexit".