A major steel supplier was frightened off working for Oxford University because of the campaign by animal rights activists, a High Court judge was told yesterday.

Oxford University returned to court in London to extend its existing injunction against activists opposed to the building of its £20m biomedical research lab in South Parks Road.

Charles Flint, for the university, told Mr Justice Holland that workmen, businesses, students and university staff had all been intimidated by the campaigners.

He said one steel contractor had pulled out of a tender on a university project not connected to the lab last week because it "feared personal and local retribution".

Police evidence showed instances of people following vehicles from the site, and known activists had been given a warning in January after a person following a contractor was intercepted four miles outside Oxford.

Mr Flint said the defendants - both named campaigners and groups - were taking steps to identify suppliers and put pressure on companies connected to the university.

The current injunction allows a demonstration opposite the site every Thursday afternoon but otherwise bans all protest activities, including the use of amplified noise or cameras, within a designated exclusion zone.

Mr Flint said an extension of the zone, to cover an area of about four square miles of university property around the site, was necessary to protect university staff, students and building contractors from intimidation and harassment.

In any event, it was "entirely reasonable and necessary" to extend it to cover the whole of three roads - South Parks Road, Mansfield Road and St Cross Road.

Mr Flint said that the existing boundaries allowed protesters to congregate immediately outside the Department of Experimental Psychology and observe contractors entering the site.

He said there was clear evidence that the defendants were determined to identify and threaten contractors, and their previous history implicated three of them - Mel Broughton, John Curtin and Robert Cogswell.

Mr Flint said that no court order would completely stop those who wished to engage in acts of intimidation or harassment, but the court should do what it could.

"It may not be wholly effective, but that is no reason for the orders not to be made."

Mr Flint also argued that a megaphone should be completely barred from protests. "This is a place of study and the use of a megaphone is not necessary," he said.

The individuals involved in the proceedings are: Mel Broughton, John Curtin, Robert Cogswell, Max Gastone, Robin Webb, Amanda Richards, Greg Avery and Natasha Avery, plus several named groups.

The hearing continues.