Some of the U.K.'s top bosses have warned their staffs about the impact of a possible exit from the European Union. The U.K. goes to the polls on Thursday to decide whether they should remain part of the EU.

After a brief pause in campaigning due to the shocking murder of a British lawmaker on Thursday, with three days to go until the vote, campaigning is back in full swing. A Financial Times poll-of-polls put the "leave" and "remain" camps neck-and-neck at 44% each.

This has given the markets something to cheer about, with the FTSE 100 recently trading up at 6,150.99, about 2% up and the pound was up 1.96% against the dollar at $1.4640.

Diageo's   (DEO) CEO Ivan Menezes today wrote to the company's 4,773 staff saying that it would be "better for the U.K., better for Diageo and better for the Scotch whisky industry that we remain in."

He added that being a part of a single market had benefitted the drinks company and warned that negotiating new trade deals could take years.

"The EU has so far concluded, or is negotiating, over 50 of these global agreement, many of which provide significant commercial benefits for Diageo," Menezes wrote.

The Society of Motor Manufacturers and Traders, whose members include Jaguar Land Rover, BMW (BAMXY) and Toyota (TM - Get Report) , backed the "remain" campaign.

The organization, which supports 800,000 jobs across the U.K. and contributes £15.5 billion ($22.7 billion) a year to the economy, warned that a vote to leave the EU would increase costs and threaten jobs.

Jaguar Land Rover CFO Ken Gregor said, "Remaining the in the EU - our largest market - will increase Jaguar Land Rover's chances to grow, create jobs and attract investment in future technologies."

Toyota's deputy managing director in the U.K., Tony Walker, said that the U.K.'s continued membership of the EU would be best for the business and its competitiveness in the long term.

BMW board member Ian Robertson said, "We firmly believe Britain would be better off if it remained in an active and influential member of the EU, shaping European regulations, which will continue to impact the U.K. whatever the decision on Thursday."

Richard Branson warned today that a "Brexit" would be "devastating" for the long-term prosperity of the U.K.

The billionaire founder of the Virgin Group wrote, "Although I've been living in the British Virgin Islands for some time now, I have never stopped caring passionately about the U.K. and its great people. I am one of the few business people who can remember how difficult it was before the EU was formed."