South-west London shopping districts were targeted by people who illegally collected thousands of pounds under the guise of animal rights activists.

Twenty-one people have been arrested in a clampdown on illegal collectors, many with links to activist terrorism.

They have been charged with collecting money without a licence on stalls around London, including Sutton, Croydon and Wimbledon.

This means the money is not subject to any audit, and is therefore untraceable and not accountable.

Metropolitan Police said much of the money funded groups linked to criminal behaviour and two stalls frequently run in Oxford Street alone made about £80,000 a year.

Many of the stalls carried flyers of Stop Huntingdon Against Cruelty (SHAC), a militant group that targets anyone with ties to the Cambridge animal-testing research company Huntingdon Life Sciences (HLS).

SHAC members are suspected to be behind a baseball bat attack that left HLS boss Brian Cass within an inch of his life, a package of lethal explosives sent to scientist Heather Saunders, and countless cases of stalking and threats in Britain and America.

The street collectors allegedly lured unsuspecting animal lovers to their stalls with "petitions" that are often never sent anywhere.

"Those collecting the money have been seen to just put the money straight in their pocket," said a Met spokesman. "Police believe this money can easily be used to fund criminality or the lifestyle of full time extreme activists."

Among the 21 arrested in London were Terence Russell and Kim Webster, both of Carshalton in Surrey, who will appear in court on April 11 over a collection in Wimbledon.

Detective Chief Inspector Tim Yarrow said lawful collectors would each wear a name tag. They would clearly display a license from the relevant authority and the charity they are promoting. If they collect more than £100, they must submit their accounts for audit.

"Therefore members of the public giving money to organisations collecting without a license ... will have no certain knowledge of how that money is then spent," said DCI Yarrow. "They may well be funding criminal activity".