Seniors traders are being asked to stay overnight in anticipation of the referendum result

Senior traders at major banks including Citigroup, JPMorgan, Goldman Sachs, and Morgan Stanley are being asked to stay overnight in the office on Thursday as Britain votes on whether to "Remain" or "Leave" the European Union in the referendum, according to The Financial Times.

"We have got an extra 30-40 people staggered across the night in London," Grant Foley, chief financial officer at CMC Markets told the FT. "We have paid for people to have hotel rooms near the offices and we will be ordering in food to keep them sustained."

JPMorgan also booked hotel rooms for its London staff, the FT says, in anticipation Friday's referendum result.

Recent polls show the result is too close to call, but global markets will be sensitive to either outcome.

Stocks are set to rise rapidly on a Remain vote. The pound will most likely get a bump against the dollar and the euro, as uncertainty clears, rising by as much as 6%, according to Bill O'Neill at UBS Wealth Management.

The pound was rallying Thursday morning, with markets seeing a stronger possibility of a Remain vote winning.

In the case of a Leave vote, market scenarios have been more apocalyptic. The pound could drop suddenly by as much as 15% or more and the FTSE 100 would most likely nosedive, according to HSBC.

George Soros, who famously made £1 billion ($1.48 billion) betting against the pound on "Black Wednesday," said "that after a Brexit vote the pound would fall by at least 15% and possibly more than 20%." On Wednesday, analysts at Credit Suisse said several factors could conspire to make the fallout even worse.

Traders in foreign exchange and interest rates markets, as well as senior management, will mainly be working the night shift, according to the FT.

To stay updated on the results, follow our live coverage of the referendum here.