A Toronto man believes he may be one of hundreds of children conceived by a single sperm donor -- and he's on a mission to track down as many of his siblings as possible.

Barry Stevens, a Toronto documentary filmmaker, was 18 when he first learned he was conceived with the help of a sperm donation through a clinic in England.

Years later, with the help of the Internet and developments in DNA technology, he began searching for his biological father.

What he discovered was stunning. DNA testing proved his father was Bertold Weisner, an Austrian Jew who ran a fertility clinic in the U.K. from 1943 to 1962.

And when Stevens began tracking down others who were conceived at the same clinic, he found many of them also shared Weisner's DNA.

"Out of 18 or 19 people from that clinic who we tested about two-thirds were his, DNA revealed," Stevens told CTV's Canada AM.

"And we know approximately they produced about 1,500 children over that period and two thirds of 1,500 is 1,000, so that's a high figure."

Stevens said there's no way of tracking down all the children who were born with assistance from the fertility clinic, so his estimate of 1,000 siblings is based on the snapshot from the group he has been able to get in touch with.

"It may be considerably lower than that, it could be considerably higher than that but it would be certainly in the hundreds," he said.

Over the past seven years, Stevens has confirmed through DNA testing and by comparisons with Weisner's natural children, that he has at least 12 siblings all sired by the biologist.

In the 1940s, 1950s and 1960s, he said, there were few laws governing fertility clinics in the U.K., and the work was done quietly because the offspring would have been considered illegitimate under British law.

In Canada to this day, he said, there is little regulation in place to prevent against one donor fathering dozens, or even hundreds, of children.

And in the recent federal budget the Conservative government announced it was cancelling the federal Assisted Human Reproduction Canada program, which regulated the industry.

"It's basically a legislative and regulatory vacuum in this area," Stevens said.

"We import sperm from the United States and elsewhere where there is very little regulation whatsoever, so it is possible there are these large numbers of half-siblings kicking around. Even in Canada I know some who are growing up together, who are friends, who don't know they're half-siblings."

He said Australia and the U.K., as well as a number of European countries, now have legislation in place that allows children born through fertility clinics to learn the identity of their biological parents.

Those laws, he said, have vastly increased accountability in the industry, but perhaps surprisingly have not reduced the number of people donating their sperm.