Former U.S. Treasury secretaries say Brexit would make Britain poorer and smaller

A British Union flag and an European Union flag are seen flying above offices in London, Britain, March 30, 2016.

US: Britain will be poorer, more inward looking and London's role as a global financial center could be undermined if it votes to leave the European Union in a June 23 referendum, eight former U.S. Treasury secretaries said on Wednesday.

"A vote to leave Europe represents a risky bet on the country’s economic future," the former U.S. Treasury secretaries said in an open letter to The Times newspaper.

The letter was signed by Timothy Geithner, Henry Paulson, John Snow, Paul O’Neill, Lawrence Summers, Robert Rubin, Michael Blumenthal and George Shultz. Their warning comes before a visit by U.S. President Barack Obama to visit Britain.

"Brexit could call into question London’s role as a global financial center. For many financial institutions, London has served as the financial springboard into Europe," the former Treasury secretaries said.

"A UK turned inward and less engaged in Europe is less able to lead on the critical challenges Europe faces."

A Brexit would disrupt trade and attempts to renegotiate agreements would be difficult, they said.

"The uncertainty surrounding Brexit already appears to be acting as a drag on investment and market sentiment, and a vote to leave could introduce an extended period of uncertainty that could hinder growth even further," they said.

"The better alternative seems to us to work for progress within the confines of EU membership, without incurring the significant economic risk of Brexit: a smaller, slower-growing British economy for years to come," they said.