A scientist may have fathered around 600 babies while running a fertility clinic in London from the 1940s through to the 1960s.
Dr Bertold Wiesner ran the Barton Clinic with his wife Dr Mary Barton. The Portland Place clinic is believed to have helped women conceive around 1,500 babies known as the 'Barton Brood'. But tests in 2007 on 18 children conceived via the clinic found that two thirds were the doc's biological offspring!
Two of his sons, London based barrister David Gollancz and Canadian filmmaker Barry Stevens, are making a documentary about children born from donor sperm, and have calculated their dad could have fathered 600 children.
David Gollancz told the Daily Mail: "It's rather uncomfortable, because artificial insemination was developed on an industrial scale for cattle and I don't like the feeling of having been 'bred'.
"But meeting the half siblings that I have tracked down has been a very life-enriching experience. This does make it frustrating too, because I know there are all those other siblings out there who I don't know but would really like to meet. I'd love to be able to hire a huge marquee and invite them all to a party.
The high fees meant most of their clients were middle-class, but Barton also claimed to have helped many of the upper classes and even some 'peers of the realm'.
The couple used family friends to provide sperm, but a shortage of donors is believed to have led to Wiesner providing the majority.
Dr Barton told a 1959 government forum on artificial insemination: "I matched race, colouring and stature and all donors were drawn from intelligent stock."
She added: "I wouldn't take a donor unless he was, if anything, a little above average.
"If you are going to do it [create a child] deliberately, you have got to put the standards rather higher than normal."
Speaking to the Sunday Times David Gollancz said: "A conservative estimate is that he would have been making 20 donations a year. Using standard figures for the number of live births which result, including allowances for twins and miscarriages, I estimate that he is responsible for between 300 and 600 children."
A fertility expert said it is 'plausible' that a man could make 50 donations a year, but legislation limits the number of times a man actually can donate, with The Human Fertilisation and Embryology Act saying that each donor can create up to ten families (but with no restrictions on the number of children per family.)
The clinic sold itself as providing sperm only 'intelligent' donors, and much of the sperm was supplied by family friends.
Dr Barton destroyed the clinic's medical records before her death in 1972.