Construction workers employed at the site reported to be at the centre of the foot-and-mouth disease outbreak may be responsible for spreading the disease, the latest report by the Health and Safety Executive has suggested.

But it fails to determine how the virus may have escaped into the environment where it could be picked up and transported by human movement.

According to media reports ahead of the final report’s official publication on Friday the exact source of the outbreak, which originated at the Pirbright site belonging to the Institute for Animal Health and used by pharmaceutical and vaccine company Merial Animal Health, may never be known.

However, it highlights a possible lapse in biosecurity at the site where construction workers were employed in a £120m redevelopment project. 

It is understood that HSE investigations found that, while staff at the two laboratories were subject to routine biosecurity protocols, no records were kept of the temporary staff working at the site. 

It raises the possibility that the tyres of a vehicle belonging to one of the workers may have inadvertently carried the disease the four miles from the site to the infected farms. 

The failure to identify a definite source of the outbreak may mean that neither the IAH nor Merial will be subject to negligence charges. 

However, a report by the BBC contradicts the views of other media sources.  In an article on its news website the BBC revisits the conclusions of the HSE’s interim report published in August shortly after the outbreak was contained. 

The BBC highlights breakages in the pipe work connecting Merial to an effluent treatment plant operated by the IAH. 

It claims that talks between Merial and the IAH are ongoing as to who owns the pipe and who is responsible for its maintenance.