The average British man or woman has indirectly slept with 2.8 million people, according to figures published today.

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An online calculator allows people to work out how many indirect sexual partners they have had based on the "six degrees of separation" theory.

The calculator, which uses data collected from more than 6,000 British adults, is being dubbed Sex Degrees of Separation by Lloydspharmacy, which developed it to raise awareness of sexually-transmitted infections.

People enter the age range of each partner and the calculator works out how many previous sexual partners people in that age range have had on average.

It then repeats the process for five further "generations" of partner to given an overall total.

Clare Kerr, head of sexual health at Lloydspharmacy, said: "When we sleep 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 STIs and take appropriate precautions including using condoms and getting themselves checked out where appropriate.

"A simple sexual health check will give both partners in a relationship peace of mind.

"The majority of STIs are easy to rectify, but if left untreated, the long term implications can be very serious."

On average, British men claim to have directly slept with nine partners each while women say they have had 6.3 partners, giving an overall average of 7.65, the pharmacy chain said.

The calculator is at www.lloydspharmacy.com/sexdegrees