Work has resumed amid tight security and the university authority is keeping the identity of the contractors and suppliers a closely guarded secret.
A police investigation was said to have found false letters to shareholders from Montpellier bosses urging them to sell or face action from activists.
The Metropolitan Police National Extremism Tactical Co-Ordination Unit was called in to investigate a campaign of intimidation against the company.
Materials supplier RMC called in police following a break-in by activists at its Ragley quarry in Dunnington, Warwickshire in June 2004.
University registrar David Holmes confirmed that assistance had been given by the police.
'I can' t give details but you can be assured there has been a great deal of security and planning,' he said.
The complex is intended to update and replace a number of existing laboratories, bringing them together under one roof. It was originally to have been built in two phases, with the first due to open this autumn.
In November last year Oxford University was granted an injunction by the High Court to protect staff and those working on the research facility from threats or acts of violence.
Peaceful protest was allowed one day a week, but not within 100 yards of the site.
Mr Holmes indicated today that the university may seek a tightening
up of the injunction to prevent disruption caused by noisy demonstrations.