A BBC investigation has found that 50 of the 74 clinics which responded to questioning had either insufficient sperm or none at all. The country as a whole has about 85 such clinics.
Donors of frozen sperm, eggs and embryos were stripped of their anonymity in April 2005, now a child born thanks to a donation is able to discover the identity of the donor once they reach the age of 18.
Previously, donor children were only able to obtain non-identifying information and to verify that they were not genetically related to their partner's family.
Donors of fresh sperm will have their anonymity lifted next year.
According to the BBC investigation, there are only 169 registered donors in the United Kingdom and none in Northern Ireland, one in Scotland and six in Wales.
Some clinics have been forced to seek stocks overseas, particularly in Spain.
In 2000, Britain had 325 donors, compared to just 157 between January and August 2005, according to figures from the Human Fertilisation and Embryology Authority (HFEA), the authority that oversees fertility treatment.
"We've seen a drop in donors but the trend was already there because of the rise of a new fertilisation technique," a spokeswoman for the HFEA said.
The new technique, intra-cytoplasmic sperm injection (ICSI), means in-vitro fertilisation for an egg with the sperm of the future father after natural attempts at conception have failed.
California has allowed publication of the identities of donors since the early 1980s. In Europe, Sweden lifted anonymity in 1984, followed by Norway, the Netherlands and Iceland.
In France, a proposal was submitted in June to create a so-called "double counter": one with identified donors, and one with anonymous ones. Future parents would be able to choose between the two.