Unlike the female pill, a male equivalent, YCT-529, is hormone-free and prevents sperm production by blocking access to vitamin A.

It's hoped that if trials are successful, the daily pill could pave the way for responsibility for contraception to be shared fairly between the sexes.

Previous versions of male birth control have tried to suppress testosterone in a bid to halt sperm production, but this was not completely effective and was linked to complications.

Studies dating back almost 100 years have shown depriving mice, rats and monkeys of vitamin A can lead to infertility - a fact which has inspired the new hormone-free pill.

Makers claim new method could be more effective than condoms

Pre-clinical studies have found YCT-529 is "99% effective and 100% reversible, with no side effects", according to experts at its manufacturer, YourChoice Therapeutics, based in San Francisco.

The new hormone-free drug is being tested by 16 British men, with the initial trial phase conducted by Nottingham-based drug development company, Quotient Sciences.

Men are currently limited to using condoms or having a vasectomy to prevent unwanted pregnancies, while women can choose from the pill, coil, contraceptive injection and female condoms or diaphragms.

According to YourChoice Therapeutics, its male pill, to be taken daily, achieves a greater contraceptive effect than condoms.

But the NHS says condoms are 98% effective when used correctly.

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'The world is ready' for a male pill

The YCT-529 pill was developed by Gunda Georg, regents professor at the University of Minnesota's College of Pharmacy.

She said: "The last innovation in contraception was the birth control pill for women, and that's more than 60 years ago.

"The world is ready for a male contraceptive agent, and delivering one that's hormone-free is simply the right thing to do given what we know about the side effects women have endured for decades from the pill.

"We consciously chose to inhibit the vitamin A signalling pathway in the testis because nearly 100 years of research has validated this pathway and shows that infertility can be reversed easily."

The pre-clinical data revealed the drug was 99% effective in preventing mouse pregnancies and decreasing sperm counts in monkeys after two weeks of dosing, Ms Georg said.

It has demonstrated a "strong safety profile" and "full reversibility" in monkeys and mice once the treatment ended, she added.

'We believe this will be more attractive to men'

Co-founder and chief executive of YourChoice Therapeutics, Akash Bakshi, added: "YCT-529 blocks a protein - not hormones - to prevent sperm production.

"We believe this will be more attractive to men, most of whom view pregnancy prevention as a shared responsibility even despite today's limited contraceptive options, which are permanent or only moderately effective.

"The dearth of options reinforces the centuries-old view that pregnancy prevention is 'a woman's responsibility'.

"It's not - and we're committed to advancing the first hormone-free birth control pill for men that's effective, convenient and temporary."

Male volunteers who would like to take part in the study are invited to contact Quotient Sciences at weneedyou.co.uk

The drug is one of a number of medications being trialled in a bid to balance responsibility and bring alternative birth control one step closer, including a male contraceptive gel and a monthly gelatine pill.

A study in March revealed women could face an increased risk of breast cancer from taking any kind of hormonal contraceptive.

Meanwhile, women who take some common painkillers, including ibuprofen, alongside the pill could increase their risk of blood clots, research has found.