Some do it to keep warm on a chilly night. Others think it might burn off a few calories after a heavy dinner. The spiritual among us might even feel it brings us closer to God.

But the main reason for having sex is seldom as straightforward as passion, it is claimed.

While love and attraction remain a clincher for some, psychologists have identified 235 other reasons why men and women want to make love.

Moment of passion, or is the story more complex?

According to the biggest study carried out into sexual motivations, these include that it is a "reasonably effective way of overcoming boredom", help you fall asleep or gets rid of a stress headache.

For others, the desire for revenge was the major factor, while some lovers were motivated by a purely selfless wish to make the other person feel good.

The researchers also confirmed what most already consider obvious - men and women think differently about sex.

They found it was more about the physical experience for men, while women's desires were based on an emotional need.

Women were much more likely to say: "I realised that I was in love." Men were more likely to say: "I wanted to increase the number of partners I had experienced."

Researcher Cindy Meston said: "We identified 237 distinct reasons why people have sex. They ranged from the mundane - 'It feels good', to the spiritual - 'I wanted to feel closer to God'.