FILE PHOTO: Goldman Sachs Chairman and CEO Lloyd Blankfein speaks at the Bloomberg Global Business Forum in New York, U.S., September 20, 2017. REUTERS/Brendan McDermid

LONDON (Reuters) - Goldman Sachs GS.N chief executive Lloyd Blankfein expects to fill the firm's new European headquarters which is currently under construction in London, but said Britain's exit from the European Union left much outside the bank's control.

“In London. GS still investing in our big new Euro headquarters here. Expecting/hoping to fill it up, but so much outside our control. #Brexit,” Blankfein tweeted on Monday, alongside a bird’s eye picture of the new building.

The Wall Street bank is building a 1.1 million square foot office in London with initial occupancy slated for 2019 to house its 6,000 UK employees, but the firm needs to ensure it can still service its EU clients after Brexit and may have limited access to the EU’s single market from Britain.

Goldman also has flexibility to adjust the number of floors it takes in the new building, according to a source familiar with the situation, so it is not committed to occupying the entire office. That option was put in place prior to the Brexit vote.

Earlier this month, Goldman said it had agreed to lease office space at a new building in Frankfurt, giving it space for up to 1,000 staff.

That would be five times the current staff of 200 and see it bolstering activities including trading, investment banking and asset management.

Blankfein sparked a wave of speculation earlier this month when he tweeted he was planning to spend a lot more time in Frankfurt.

“Just left Frankfurt. Great meetings, great weather, really enjoyed it. Good, because I’ll be spending a lot more time there. #Brexit,” he tweeted on Oct. 19.

Frankfurt is so far seen as the biggest beneficiary from Wall Street banks moving jobs out of London as a result of Brexit, with JPMorgan, Citi and Morgan Stanley all setting out plans to expand operations there.