Five cars parked outside the homes of employees of Huntingdon Life Sciences in the village of Godmanchester, Cambridgeshire, were set on fire by animal-rights activists. A sixth attempt failed.

A spokesman for the centre said: "It is extremely fortunate that nobody was hurt or killed,but they certainly created a lot of damage." Security at the centre had been increased in recent months, he said, but protecting employees in their homes would be difficult.

The staff affected were not all involved in experiments on animals, he said. "We don't know exactly why these people were targeted, but we do know that some of their names and addresses have been included in campaign propaganda written against us."

The centre carries out experiments on rats, rabbits, dogs and cats to develop medicines. "The Government insists that such experiments take place," the spokesman said. "It is fully regulated."

Cambridgeshire police said it was the second spate of arson attacks on the cars of people connected with the centre.