British Prime Minister Gordon Brown was waiting for a second report yesterday on Britain's foot-and-mouth (FMD) outbreak after an initial probe fingered human activity at a laboratory as the most likely cause.
The Health and Safety Executive (HSE) said there was a "strong probability" the leaked strain came from the Pirbright site south-west of London, adding it was a "real possibility" that human movement spread the disease to two nearby farms.
The chance of FMD being spread by flooding or aerial transmission was dismissed as "negligible."
Environment Secretary Hilary Benn admitted the government had to consider the possibility of deliberate human contamination.
"The truth is, we don't know. We're all very very anxious," he said.
The HSE report did not blame either of the organizations which share Pirbright -- the state-funded Institute for Animal Health (IAH) and the private animal pharmaceutical firm Merial.
It found the out-of-circulation disease strain, first confirmed in cattle on Friday, was being worked on last month in "large scale production" involving 10,000 liters by vaccine-producing Merial and "small scale experiments" involving less than 10 milliliters by the IAH.
National Farmers' Union president Peter Kendall, aghast at the high probability that a facility working to protect against disease was the outbreak's source, said the NFU would consider a legal challenge for compensation.
"If this turns out to be a commercial company, that has been and can be shown to have been careless in any way, my members are already very loudly saying `we've lost money, our businesses are no longer able to function, we've got animals, extra feed costs, problems with capacity being squeezed on farms,'" he told BBC television.
"There are many, many costs that have been incurred by farmers through no fault of their own," he said.
The HSE report identified a "number of biosecurity issues" surrounding Pirbright's effluent treatment system.
HSE chief executive Geoffrey Podger said that Merial faces more questions, notably to do with its drainage facilities.
"Our assessment is that there is no reason to prevent the IAH from operating providing that all the usual biosecurity protocols are followed rigorously," he said.
"In relation to Merial, we advise that further work be done before any operations involving live pathogens are restarted," Podger said.
Merial has nonetheless been asked temporarily to restart production of FMD vaccines and manufacture 300,000 doses in case the disease spreads further.
As Britain scrambled to prevent a repeat of 2001's crippling epidemic, the second report Brown hoped to see published yesterday was expected to clarify further how the virus got to cattle grazing near Pirbright.
The facility is 5km from the farm where FMD was initially confirmed.
Approximately 200 animals have been slaughtered and incinerated so far.
The Daily Telegraph newspaper said officials were investigating a further 20 possible cases of FMD thought to be close to the center of the outbreak.