That's according to law company Brabners Chaffe Street, which predicts the UK economy will take a £4 billion hit because of lost productivity if 50% of workers spend an hour a day looking at football-related websites during the tournament.

Spokesman Joe Shelston said:

"The danger for employers is that they assume that so long as their workers are at their desk, there is no problem.

"With much more entertaining websites and chatrooms than there were four years ago, football fans are going to find themselves spending more and more time online when they should be working."

The legal experts say that employers must clarify to staff what is acceptable behaviour and what isn't before the tournament starts.