Two government reports cite a combination of events involving leaking pipes, heavy rainfall and failure to monitor construction vehicles at the Institute of Animal Health site in Pirbright, Surrey, as possible causes of the Foot and Mouth Disease outbreak.
The Health & Safety Executive and Professor Brian Spratt from Imperial College, London were both commissioned by Defra to look into the source of the FMD outbreak.
HSE chief executive Geoffrey Podger said that his investigation established that it was possible for the live virus strain - O1BFS - to enter the site effluent drainage system. "We judged it likely that waste water containing the live virus, having entered the drainage pipework, then leaked out and contaminated the surrounding soil.
"This conclusion is supported by evidence of long term damage and leakage, including cracked pipes, tree roots breaching pipework, and unsealed manholes. We also believe that excessive rainfall in July may have increased the potential for virus release from the drain."
His report also highlighted that during the period of the HSE investigation both human and vehicle movements at Pirbright were not adequately controlled. "We conclude that failure to keep complete records was not in line with accepted practice and represents a breach in biosecurity at the site.
"In particular, vehicles associated with ongoing construction work had relatively unrestricted access to the site. In our opinion, these construction activities - very near to the effluent drainage system - are likely to have caused disturbance and movement of soil in a way that contaminated some of the vehicles with the live virus.
"We established that some of the vehicles, probably contaminated, drove from the site along a road that passes the first infected farm."
Podger concluded that this combination of events was the likely link between the release of the live virus from Pirbright and the first outbreak of FMD.
Professor Spratt's report also said there was very little doubt that the FMD outbreak was caused by FMD virus from either the Institute of Animal Health (IAH) or Merial Animal Health. The main focus of his concern, he said, had been the old, poorly maintained and defective effluent system that is shared by the IAH and MAH, which should have been fully contained and was not.
Hilary Benn, secretary of state for Environment, Food and Rural Affairs said: "The thorough and detailed work carried out by the HSE and Professor Spratt shows that there is no absolute certainty about how the outbreak occurred and no one single factor can account for it."
He added: "Everyone who is involved - the management and staff of the IAH and Merial, Defra as the licensing authority and regulator and BBSRC as the owners of the Pirbright site and sponsors of IAH - must take careful note of the conclusions of these reports and act swiftly to put right every weakness that has been identified.
Stuart Roberts, director of the British Meat Processors Association, said: "The fact that a lab who's primary purpose is to improve the health of animals is the probably cause of the outbreak give cause for significant concern. "We along with a host of others will be going through the reports in detail.
"The priority now is that every action is taken to prevent anything like this happening again."
Shadow Environment Secretary Peter Ainsworth said: "In the early stages of the outbreak, the Government's spin machine went into action to try to pin the blame for the release of the virus on Merial and not their own laboratory. It is now clear that it was poor maintenance at IAH that was the likely cause and that, though warned "several years" ago about the state of the drains, the Government failed to make funds available to fix them. In any case, the whole site is subject to inspection, regulation and licensing by Defra.
"It is staggering that farmers will find not the slightest shred of an apology from Defra in its response, despite the fact that the outbreak has cost the industry tens of millions of pounds. Nor is it clear who is actually shouldering responsibility for the breaches of biosecurity.
"We welcome the inquiries that are now to be set up, but their scope is a tacit admission of a shameful failure of supervision and effective action."
Defra had today also published a further epidemiological report into the outbreak in Surrey. The chief veterinary officer Debby Reynolds announced that she was satisfied the FMD had now been eradicated from Surrey.
The Surveillance Zone around the infected premises will be lifted at noon tomorrow. Restrictions outside the Surveillance Zone, will be lifted at the same time. This includes a 20-day standstill for livestock following movement and additional controls on livestock markets and shows.