Mrs Blood, 30, pleaded for an explanation, and yesterday, in a letter faxed to her parents, the HFEA said her husband had not given specific consent for his sperm to be exported.
The organisation was "reluctant" to rely on someone else's evidence that he ever gave any consent.
The letter stated: "After careful and full consideration occupying two- and-a-half hours of discussion and notwithstanding its sympathy for Mrs Blood, the authority decided not to exercise its discretion to allow the export of the sperm."
The HFEA said her husband's written consent was required after he had gone through counselling. But this had not happened.
Yesterday, it emerged that the British Medical Association's ethics committee urged the HFEA to reject Mrs Blood's attempt to have a baby using her dead husband's sperm.
In an unsolicited letter to the authority's chairwoman, Ruth Deech, prior to Thursday night's decision to confirm the ban on the treatment either here or abroad, the committee's chairman, Dr Stuart Horner, suggested that Stephen Blood, the husband, had not properly thought through the full implications of a child being created after his death.
Dr Horner's letter, dated Tuesday, said that informed rather than written consent was the real issue. "We believe that the doctrine of informed consent, which is central to medical ethics, must not be eroded," he wrote. "Ethically, whether the consent is in writing or given orally is irrelevant. The essential issue is the quality of consent ... it appears [Mr Blood] made a passing comment whose validity is difficult to evaluate in retrospect."
The letter added that since it was unacceptable to use the sperm without consent in this country, it was equally unacceptable for it to be used abroad.
Paul Plant, co-ordinator of the Stephen Blood Baby Appeal, said: "Diane is disgusted and very, very upset about these comments. This gentleman is doubting ... her evidence. He should have ensured he was in possession of all the facts."
Mrs Blood was facing a fresh crisis yesterday as her supporters said that pounds 50,000, in addition to pounds 15,000 already received in donations, was urgently needed for a court appeal in January.
The authority confirmed that the frozen sperm, now 18 months old but with a shelf-life of 30 years, would continue to be safely stored until all legal avenues had been exhausted.
The fertility expert Lord Winston, a Labour peer, introduced a backbench Bill this week to amend the law - but this is unlikely to make progress within the life of this parliament without government backing. He said yesterday that ethics were never fixed and the BMA committee had "let Mrs Blood down".
The Stephen Blood Baby Appeal can be contacted on 0121-643 4636.Reuse content