Visits to online betting sites by UK workers are up 73 per cent this week ahead of Saturday's Martell Grand National, according to statistics from ScanSafe. 

The web security firm polled almost one billion web requests during the first few days of April, and saw a dramatic surge in employees visiting online betting sites during office hours.

ScanSafe claimed that one of its corporate customers had a member of staff who spent close to two hours on one particular site.

"These statistics may cause concern for many organisations, as they illustrate that employees are increasingly using the internet for personal reasons," said Eldar Tuvey, chief executive at ScanSafe.

"Recreational surfing at work can open up potential security risks by exposing companies to inappropriate content, web viruses and spyware that can potentially steal confidential information and passwords."

ScanSafe's report found that around 40 per cent of users now spend around an hour a day on recreational surfing.

The company claimed to have real-life examples of how this behaviour had almost led to security breaches.

"Recently we have protected a number of our customers from Trojan threats being distributed through some dubious gambling sites which can modify users' desktop settings," said Tuvey.

Anyone looking for tips for Saturday's race at Aintree might want to take the company's research into account, as ScanSafe found that last year's winner, Hedgehunter, was the most widely searched-for horse on the web. 

"Hedgehunter is the possible favourite for the race, so it seems that employees are now using the web to study racing form as well," said Tuvey.

The top five betting or gambling websites accessed by UK employees during work hours, in order of highest visits, were Betfair, Ladbrokes, Racing Post, William Hill and Coral.