A clampdown on illegal money collectors in public places has resulted in 21 people being charged.
They are accused of collecting money without a licence on stalls around London under the guise of animal rights activists.
But the Metropolitan Police said much of the money funded groups linked to criminal behaviour.
Last month four people pleaded guilty to charges of collecting money without a licence in central London.
Encouraged donations
Anyone who collects more than £100 from the public requires a licence from the Metropolitan Police.
Those charged during the clampdown worked on stalls which invited members of the public to sign petitions supporting animal rights, before encouraging them to make donations.
They collected money at locations including Sloane Square, Knightsbridge, Barnet, Sutton and Croydon.
Police estimate that two Oxford Street stalls collected about £80,000 a year.
Detective Chief Inspector Tim Yarrow, of the Public Order Crime Unit, said many public collections were legal.
"In those cases each person will have identification, they will hold and display a licence obtained from the relevant authority and they will have their promoters' details clearly on display," he said.
But he added that people donating to unlicensed organisations "will have no certain knowledge of how that money is then spent and they may well be funding criminal activity".