Four refrigerated lorries were badly damaged in the attack in Brighton, East Sussex, and a number of gas cylinders exploded. Twenty firefighters dealt with the blaze, but no-one was hurt.

John Hunt: The ALF has told the BBC it is stepping up attacks on refrigerated lorries

Police said lemonade bottles found at the scene were being tested to establish whether they had been used as petrol bombs.

A spokesman for the Animal Liberation Front (ALF) said members of the organisation were "almost-certainly" responsible.

He said the attack could mark the start of an increase in activity by animal rights activists.

The spokesman said: "ALF members are almost certainly behind this attack.

A fireman takes photographs of the devastation

"There have been a number of small incidents in recent weeks and this may be the start of an escalation in activity."

Vivisection campaign

The attacks are thought to be linked to a campaign to persuade the government to end vivisection.

The campaign is being led by Barry Horne, from, Northampton, who is serving an 18-year jail sentence for an attack on Boots chemists in the Isle of Wight four years ago.

Horne says Prime Minister Tony Blair has gone back on promises to review government policy on vivisection.

He has staged a series of hunger strikes to put pressure on ministers.