Goldman Sachs has hired José Manuel Barroso, the former head of the European Commission, to help it through the fallout from the UK's shock decision to leave the EU.

The Wall Street investment bank announced on Friday that Mr Barroso was joining as non-executive chairman of London-based Goldman Sachs International (GSI), the bank's largest subsidiary. He will also be an adviser.

Mr Barroso, who presided over the commission for a decade, said he would do what he could to “mitigate the negative effects” of the referendum decision. If the UK loses access to the EU single market, US banks may need to move big parts of their large European businesses out of London.

“Of course I know well the EU, I also know relatively well the UK environment,” Mr Barroso said. “If my advice can be helpful in this circumstance I’m ready to contribute, of course.”

The former Portuguese prime minister led the commission from 2004 until 2014, a period that included the financial crisis. He was a key figure in many of the financial sector policies that followed, including banking union.

"His advice and counsel in this time of monumental change and uncertainty . . . will be very important," said Peter Sutherland, who stepped down as chairman of GSI in May 2015. Since then, the post has been filled by GSI non-executive director Claes Dahlbäck.

Mr Barroso would not speculate on whether banks based in the UK would be able to continue to use their UK licences to do business in the EU’s markets.

He would not be drawn on alternative locations for Goldman Sachs but said he believed London would remain “very important”. – Copyright The Financial Times Limited 2016