A post-mortem revealed evidence of Creutzfeldt-Jakob Disease (vCJD) in the spleen, despite the patient not displaying any symptoms.
The patient, who was over 70, is the first haemophiliac to be identified with vCJD, and died of an unrelated condition.
He was treated with several batches of clotting factors sourced in the UK before 1999, when tighter blood controls were introduced due to fears over mad cow disease.
The Health Protection Agency (HPA) said it was working with the UK Haemophilia Centre Doctors Organisation to inform all patients with bleeding disorders of the finding, and had launched an investigation.
In 2004, all patients with bleeding disorders treated with UK-sourced pooled plasma products between 1980 and 2001 were classed as 'at risk' of vCJD due to the possibility of infection.
Professor Mike Catchpole, director of the HPA's centre for infections, said: 'This new finding may indicate that what was until now a theoretical risk may be an actual risk.
'We recognise that this finding will be of concern for persons with haemophilia. The priority is to ensure that patients are informed of this development and have access to the latest information and specialist advice.'
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