Brits have 'indirect sex' with 2.8million people

A new internet calculator allows people to work out the total number of indirect sexual partners they have had over their lifetime.

Men claim to have had an average of nine sexual partners while the average women admits to 6.3 lovers, giving an overall average of 7.65.

However, experts claim that by having unprotected sexual intercourse, people are potentially exposed to the sexual infections of hundreds of thousands of others.

The calculator has been developed by national chemist chain Lloydspharmacy to help people understand the risks of unprotected intercourse.

According to the Health Protection Agency, cases of sexually transmitted infections rose last year by half a per cent to 399,738 and cases of chlamydia increased by eight per cent between 2006 and 2008.

The calculator, which uses data collected from more than 6,000 British adults, is called 'sex degrees of separation', a reference to the famous theory first proposed by Hungarian writer Frigyes Karinthy which states that no one is more than six steps removed from another.

When people enter the age range of each partner, the calculator uses its database to work out how many previous sexual partners people within that age range have had on average.

It then repeats this process for five further 'generations' of partner. This is added together to give a sex degrees of separation total.

The launch of the calculator coincides with the introduction of Lloydspharmacy's Relationship Screen, an online postal service which allows people and their partners to be tested for chlamydia – the most common sexually transmitted disease – gonorrhoea and HIV before committing to full intimacy.

Clare Kerr, head of sexual health at Lloydspharmacy said: "When we have sex with someone, we are, in effect, not only sleeping with them, but also their previous partners and their partners' previous partners, and so on. "It's important that people understand how exposed they are to sexually transmitted diseases and take appropriate precautions including using condoms and having checks when necessary.

"A simple sexual health check will give both partners in a relationship peace of mind. The majority of sexually transmitted diseases are easy to rectify, but if left untreated can have serious implications.