Monogamy is outdated and “polyamorous” relationships, involving multiple partners, could become the new normal, according to a controversial BBC investigation.

Monogamy and the Rules of Love, a Radio 4 documentary broadcast on Monday, features a pair of co-habiting couples, living together in Sheffield, who use a Google calendar to plan when they have sex with each other.

The programme argues that the “taboo” around sharing lovers between an unlimited number of sexual partners could disappear within a decade.

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Presenter Jo Fidgen interviews experts and meets British couples who have rejected monogamy. “Could monogamy really lose its moral monopoly inside ten years?,” she asks.

She meets Charlie, a woman who has been married to Tom for six years. Before their marriage, Tom met and fell in love with Sarah, with Charlie's approval.

Subsequently, Sarah and Charlie also began a relationship. Then Sarah got engaged to a man called Chris. “And somewhere along the line I fell in love with Chris and now we're all planning to grow old together,” Charlie tells the programme.

Some Radio 4 listeners may be shocked by the frank discussion of partner-swapping, which will follow The Archers.

Charlie explains: “We use a Google calendar to keep track of date nights. Who gets the TV and who is in what bedroom.”

She says: “It's not like there's only so much love I've got to give and I only want to give it to one person. I can love as many people as I can fit into my heart and it turns out that's quite a few. I don't think there's a limit on that.”

But Ms Fidgen speaks to Esther Perel, a Belgian sex therapist with a radical approach to relationships, who predicts that the “power” of monogamy is subsiding.

Perel agrees that “multi-partner relationships are coming on the radar” and suggests that they will become common within 30 years, if not ten.

“Monogamy has shown remarkable endurance. These relationship pioneers are revising the rules of love to promote sexual honesty over exclusivity,” Ms Fidgen said. “If they persuade people there's a viable model then monogamy becomes a choice rather than the default.”

She asks: “Does true love really mean forsaking all other lovers? Most of us assume a conventional serious relationship depends on sexual fidelity. What happens when we open our minds and our relationships?”

The programme quotes a British social attitudes survey which found that 80% still believe that it's wrong to stray. But Ms Fidgen speaks to Esben Esther Pirelli Benestad, a Norwegian sex expert with a radical approach to relationships, who predicts that the “power” of monogamy is subsiding.

Pirelli agrees that “multi-partner relationships are coming on the radar” and suggests that they will become common within 30 years, if not ten.

The programme does not examine the effect of “polyamorous” households on children. Ms Fidgen said she didn't want to “get into a debate about what's best for society or whether we are genetically programmed to have one partner or many. We're looking at the rules of love. All lovers want the same thing - to be happy.”

She said: “We don't see any contradiction in loving more than one friend. No-one asks us to only love one of our children. Why shouldn't it be any different with romantic love?”

The documentary does examine how couples in “open relationships” cope with jealousy. Charlie said she was “so happy” when her husband fell in love with Sarah. The women said they ask permission from their three partners before they go on a “date” where they may discover a new potential sex partner.

Another participant, Alice, interviewed for the programme, says she would be happy to leave her male partner to look after the children while she goes out seeking casual sex.

'Monogamy and the Rules of Love', Radio 4, 8pm, Monday August 19