A judge has refused to create an exclusion zone to keep animal rights protesters away from Oxford's Sheldonian Theatre during graduation ceremonies.

Oxford University had asked for the ban to stop protesters against its new animal testing laboratory disrupting proceedings, saying shouts from demonstrators ruined the "peace and quiet" of the occasion.

But Mr Justice Treacy, sitting at the High Court in London, said yesterday there was no evidence to prove that protesters had posed any threat to students during the ceremonies.

However, the judge did extend the exclusion zone around the nearly-completed laboratory, in South Parks Road, by a further 100m, so protesters could not harrass students, academics and lab workers.

He said that, during the construction of the laboratory workers had been protected, but on its completion he concluded that staff and students would be exposed to threats from activists, some of whom had launched violent attacks against the university.

He said: "Unless protected, I am satisfied to a high degree of probability that intimidatory conduct would result from the unrestrained gathering of protesters.

"There is a high probability that unlawful harassment... will take place unless restraints are put in place."

Extremists have made threats and attacked university property during the course of the lab's construction - and even vowed to dismantle the building "brick by brick".

However, the university has stated that it would not be intimidated by threats of violence.

A university spokesman said: "We're pleased the court recognised the need to extend the exclusion zone slightly, noting this represents the necessary and proportionate extension.

"As an institution deeply committed to freedom of speech, we respect the right to protest and to make views heard within the law.

"However, we will protect our staff and students - and those working with us - from harassment and intimidation while going about their lawful business.

"The university remains firmly committed to the completion of a new facility to rehouse animals used in potentially life-saving research. The safety of staff, students and others remains the number one priority."

A spokesman for animal rights group Speak was not available for comment.