There has been a "probable" new leak of the foot and mouth virus at the government-owned Pirbright site in Surrey.
Environment secretary Hilary Benn told MPs today a leaking valve meant it was possible the live foot and mouth virus had escaped into drainage facilities at the Merial facility.
However, he said officials from the Health and Safety Executive (HSE) and Department for Environment, Food and Rural Affairs (Defra) had been "assured" the live virus has been contained and not entered the environment.
The Pirbright site, also home to the Institute for Animal Health, was at the centre of a foot-and-mouth outbreak in August.
It is thought the virus escaped through a leaking valve in the decontaminated system. The potential leak was discovered on November 19th when Merial officials noticed a shortfall of the virus returned from production batches.
Officials found a malfunctioning valve in the vaccine production equipment, allowing the "unintended probable release" of the live foot and mouth virus into the contained drainage system.
In a written statement to parliament, Mr Benn said: "The extensive layers of biosecurity that we require under the specified animal pathogens order (SAPO) licence effectively contained the virus in the closed, re-lined drainage system before deactivation in the chemical treatment facility."
Defra was informed of the situation on November 20th and immediately suspended Merial's SAPO licence.
Merial only obtained its SAPO licence on November 6th after Defra and HSE officials were satisfied with biosecurity upgrades introduced in the wake of August's outbreak.
The facility had been ordered to improve its waste treatment and drainage systems after the live virus was allowed to leak into the environment, contaminating cattle on neighbouring farms.