A pioneering British scientist may have fathered up to 600 children at a controversial London fertility clinic he set up with his wife in the 1940s.
Bertold Wiesner is believed to have been one of the primary donors for the Barton Clinic, which helped women conceive around 1,500 babies, between the early 1940s and the mid-1960s.
The staggering claim has been made by two men conceived at the clinic who discovered they are his biological sons.
Documentary maker Barry Stevens, from Canada, and London-based barrister David Gollancz tracked down 18 other people conceived at the clinic and found that 12, two thirds of those tested, were also fathered by Dr Wiesner.
From the results, Stevens and Gollancz argue that Wiesner, who died in 1972, must have fathered as many as 600 children.
Mr Gollancz told the Sunday Times: '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.'
If Wiesner did father 600 children, it would beat all previous records - with an anonymous American sperm donor who fathered 150 children currently being the highest known figure.
Allan Pacey, an expert in male fertility at Sheffield University and chairman of the British Fertility Society, told the newspaper the calculation was 'plausible' as a healthy male could make up to 50 donations a year.
Mr Stevens believes the figure could even be as high as 1000 as the clinic was known to use only a small number of intelligent donors selected out of Dr Wiesner and his wife Mary Barton's friends.
In 2001, it was revealed Derek Richter, a neuro-chemist, fathered more than 100 of the clinic's children.
After the British Medical Journal published an article from the couple on their work in 1945, a peer in Britain's House of Lords denounced their activity as 'the work of Beelzebub' and the then Archbishop of Canterbury called for their clinic to be outlawed.