The body that oversees the sperm donor register in the UK has refuted claims a change in the fertility law is deterring men from donating.
Sperm supplies in some areas have declined
Since April 2005, UK sperm donors have had to waive their right to anonymity.
The law change has been blamed for the current situation in the Thames Valley where only one man's sperm is available through the NHS.
But the Human Fertilisation and Embryology Authority says it is a "myth" the change has caused a decline.
It has been claimed the lack of sperm donors across Oxfordshire, Berkshire and Buckinghamshire is forcing prospective parents to look abroad or at online firms.
Consultant gynaecologist Dr Tim Childs, of the fertility clinic at Oxford's John Radcliffe Hospital, said recently the law change had put men off.
But HFEA spokesman John Paul Maytum cited Manchester as an area where supply outstrips demand.
He said: "Our figures show that it's a myth that the change in the law has caused a sudden fall in sperm donors. What we see is a patchy provision across the country."
Dr Childs has encouraged more men to donate, although donors no longer get paid and are only entitled to travel expenses.
But Mr Maytum, who said the average sperm donor is not a student but now an "altruistic" family man in his 30s, said improvements in IVF conception rates mean there is less reliance on an abundance of donors.
He added: "Some areas are struggling but other areas have plenty. We'd like to see clinics in area where there is a shortage talking to other clinics where there is a good supply."