The internet is a gateway to other relationships

Angela Sibson, Relate

"People are spending too much time on the internet and that is time they are not giving to their partner," she said.

But it is not just addiction to surfing that is causing problems. There was plenty of temptation online that was causing people to stray, said Ms Sibson.

"The internet is a gateway to other relationships. They can be very potent and break up existing relationships."

Virtual love more fun

Online infidelity was much easier than a real affair she pointed out, as the perpetrator was sitting in their own house and did not have to come up with excuses for meeting their new love.

Virtual relationships can also seem a lot more fun.

"You can be who you want to be on the net and you don't have to face up to the responsibilities of a real-time relationship," explained Ms Sibson.

The highest at-risk group were the 25 to 35 year olds, people who were embarking on serious relationships but who were also most likely to be regular internet users, said Ms Sibson.

Advice by email

Relate advises net-savvy couples to get back to basics with face-to-face communication and openness about what they are doing online.

My wife of 10 years had an affair with a guy she met on the internet, ironically after I had shown her how to use it

News Online reader

Perhaps ironically, it is also hoping to offer an online relationship advice service in the coming months.

It follows a flood of e-mails to the Relate website asking for help with internet-related problems.

E-mails sent to BBC News Online bear out the danger the net can pose to relationships.

"My wife of 10 years had an affair with a guy she met on the internet - ironically after I had shown her how to use it. We are still together and trying to sort our life out," one reader confessed.

Another man expressed his frustration about the amount of time his wife was online.

"I use the internet, but I can happily live without it. I just wish this was the case with my wife," he wrote.

"When she gets in from work, the PC goes on and it can be five or more hours before she logs off. Our marriage is suffering as a result, as is her relationship with her son," he said.