The Liberal Democrat defence spokesman, Menzies Campbell, claimed that strains of the bacteria were sold during the late 1980s to an American company which sold them on to the Iraqis.
The Ministry of Defence last night denied involvement, and said the material had come from a Department of Health facility next to its own Porton Down site.
Mr Campbell said that the lives of British soldiers had been at risk in the Gulf from weapons developed by their own military establishments.
In a Commons debate, he cited an investigative report in the Washington Post which said the Iraqis had also tried, without success, to buy the deadly pathogens directly from Porton Down in 1988. However, the American Type Culture Collection (ATCC) had been able to buy them and pass them on.
The article said that the head of Britain's germ warfare programme had obtained the materials from an academic researcher and sent it to an aide who later sold it to the American repository in Rockville, Maryland.
It was well known at the time that ATCC was re-exporting pathogens freely, Mr Campbell told MPs, and obtaining materials from the firm was a simple matter.
Its customers had to submit a written request on headed notepaper, agree to accept responsibility for the material, demonstrate scientific literacy in a short telephone conversation and pay a $78 fee - equivalent to about pounds 46 at today's exchange rates.
"Recent events when the UK forces were deployed to the Gulf, where their lives might have been at risk show the price is currently being paid for the failures of the Conservative government in this matter," Mr Campbell said.
Answers to Parliamentary Questions had shown that the Department of Trade and Industry did not know whether any anthrax or other pathogens were exported to Iraq because no records were kept, he said. Lists attached to the Scott report were full of holes, and there was no way of knowing precisely which chemicals or pathogens were sold.
However, it was known that in the mid to late 1980s Iraq made numerous attempts to buy the ingredients of chemical weapons from Britain many of the export licenses were blocked, some were not.
In 1985, Iraq imported small quantities of chloroethanol and potassium fluoride, precursors to up to six different nerve gases. Between 1987 and 1988, 39 tons of growth media for biological weapons were exported by two companies.
Answering the debate, which was brought by the Liberal Democrats, the Foreign and Commonwealth Office minister Tony Lloyd promised to investigate the allegations.
"We do have to make sure we move forward to a regime that prevents this from ever happening again and staining the honour of this nation," Mr Lloyd said.
A spokeswoman for the Defence Research and Evaluation Agency, which runs the chemical and biological defence establishment at Porton Down, referred the matter to the Department of Health. The incident related to its Centre for Applied Microbiology and Research next to the site, she said. The Department of Health could not immediately confirm or deny the claim.