By David Shukman and Pallab Ghosh
Science correspondents, BBC News
Investigators say the virus that led to the foot-and-mouth outbreak in Surrey had probably been present in a pipe on the nearby Pirbright laboratory site.
The outbreak triggered a nationwide ban on livestock transports
Health and Safety Executive findings, given to the BBC, identified biosecurity lapses at the site.
It said the pipe, which runs from pharmaceutical firm Merial to a plant operated by a government-run lab, may have been damaged by tree roots.
Merial said it could not comment until the report was officially published.
It said it "cannot speculate on pipes or anything else".
It is believed the pipe may have been damaged by tree roots before flooding pushed virus traces to the surface.
It is not known how the virus found its way on to farmland a few miles away following the flooding on 20 July.
But the HSE investigation did establish that contractors working at Pirbright at the time travelled to and from the site using a country road adjoining the farmland where the first outbreak was detected in August.
A Merial spokesman said: "The report comes out on Friday. [Until] that comes out and we know what's what - and there's no way we'll know before then - we can't speculate."
The Department for Environment, Food and Rural Affairs (Defra) said it did not comment on leaked reports, but a spokeswoman said: "There are lessons for all of us to learn."
The Pirbright lab complex is shared by the Institute for Animal Health (IAH), an international diagnostic laboratory, and the private pharmaceutical company Merial Animal Health.
Experts were sent to the Pirbright site after it emerged that the strain of disease being studied there was the same as the one that infected cattle at a farm in Guildford at the beginning of August.
The BBC understands that ongoing talks are taking place between Merial and the government about whose responsibility it is to maintain the pipe.
There is also concern that worries about the condition of the pipe escaped the notice of government inspectors who licensed the laboratories.
A broader investigation by leading scientist Professor Sir Brian Spratt has highlighted a lack of co-ordination in bio-security between Merial and the IAH.
The Defra spokeswoman said she would not comment on speculation about the investigations.
"These reports will be published in full on Friday alongside a statement of the further actions that the government will be taking in the light of these reports," she said.
Michael Jack, the Tory chairman of the Commons committee on environment, food and rural affairs, said he was alarmed by the apparent findings.
"I would have thought that on a sensitive site like Pirbright, biosecurity would have been addressed in terms of looking at every way in which material on the site comes in and leaves - whether it be by a lorry, people, pipes or any other means," he told BBC Radio 4's World At One.
"I think this report shows a disturbing - perhaps - lapse in investigating all the ways in which material went in and out of this particular site.''
The disease outbreak became apparent on 3 August in a herd of cattle kept by farmer Roger Pride in fields at Normandy, near Guildford.
A neighbouring herd at Woolford Farm tested positive a few days later.
Peter Kendall, president of the National Farmers' Union, said there must never be another outbreak.
"Farming has been dramatically affected. Our export markets [and] our movement of animals within the UK [have] been shut down for quite a long period of time."
He said he had talks with Prime Minister Gordon Brown on Wednesday.
"What I said to him, quite bluntly, was we must make sure that the investment takes place to make sure this never ever happens again to the farming industry," he said.