Britain's national sperm bank has urged men to prove their manhood and donate sperm with a new 'superman' campaign – after admitting it has just nine registered donors.

A year after it was established the UK's national sperm bank has failed to take off, and chief executive Laura Witjens has revealed the new campaign starting in September is a copy of the booming sperm banks of Denmark which market themselves by appealing to male vanity.

She told The Guardian: 'If I advertised saying 'Men, prove your worth, show me how good you are', then I would get hundreds of donors.

Britain's national sperm bank has urged men to prove their manhood and donate sperm

'That's the way the Danish do it. They proudly say, this is the Viking invasion, exports from Denmark are beer, lego and sperm. It's a source of pride.'

Witjens said the 'superman' theme to be used by her promotional campaign had a serious message - donors must ideally have exceptionally strong sperm in order for it to have the best chance of surviving the freezing and thawing process.

That is one of the reason the clinic has so few on its books after almost a year. Ms Witjens said if 100 men come through the door, around 10 will come through the screenings and on average only one will actually becoming a donor.

Getting an approved donor on the books requires a man to come to the clinic twice a week for up to four months, refraining from sex or masturbation for two days before each visit and then be tested again after six months. And they are paid just £35 a session.