Solo sailors should beware of a new psychological danger which could affect their ability to navigate on a laptop. Boffins have discovered in the world’s first survey on internet use that computer users addicted  to surfing websites are five times more likely to suffer from depression than non-addicts.

Twice as many people in Britain are addicted to surfing the internet than gambling, researchers claim. Young people are most at risk, with the average age of addicts just 21, the study found. It also warned of the dangers of social networking sites if they replaced conventional interaction.

The University of Leeds survey focused on the internet habits of 1,319 people aged between 16 and 51, and found 1.2 per cent of them were hard-core internet users who could be classified as ‘addicts’.

That is twice as high as the 0.6 per cent of people in the general population who are addicted to gambling. They also had a ‘depression score’ five times that of non-addicts.

Leeds University’s Dr Catriona Morrison said: ‘If it’s interfering with daily activities, if you think about the internet when you’re doing something else, if you can’t stop doing it – compulsive behaviour -that’s problematic.’