That leaves just under five million Brits toughing things out with a partner they secretly wish was someone else.
Proving that love isn't always as it is in the movies, the poll of 3,000 people found that one in four aren't happy in their current relationship and, of those who are content, more than 50 per cent confessed to having feelings for someone else.
Perhaps most disconcerting of all is the news that one in six of these will listen to their heart (or feelings of lust, one or the other) and have an affair. If you've been the victim of a cheating partner, you may (or may not) take comfort from knowing that it usually happens just the once.
A spokesman for OnePoll.com, which carried out the research, said: "The research shows just how many people believe that it's possible to hold feelings for more than one person.
"Even in a happy relationship, it seems to be possible to have a wandering eye or even crave affection from another person."
Work colleagues, friends and exes are high on the list for those considering an affair and on average, these yearnings last for three years and three months.
It may not come as a total shock to discover that men are definitely more prone to a wandering eye, with 22 per cent claiming they were in love with two women, compared to 15 per cent of women. Almost a third of these men said they were planning to leave their partner for someone else, while only 19 per cent of women in a similar position admitted they were also looking to escape.
The spokesman added: "Men have a bad reputation when it comes to eyeing-up other women and the research proves this is actually true.
"Men are much more likely to 'window shop' whilst in a loving relationship as well as falling for another woman. And the study shows chaps are more likely to stray too."