People who hand over cash to beggars on the streets of Brighton and Hove are unwittingly funding the drugs trade.
A survey has revealed many spend the handouts on heroin. Some beggars collect more than £200 a week.
Police have warned those who give cash that they are putting their money into the pockets of drug dealers.
More than a third of the 30 regular beggars quizzed by police for the survey admitted they spent the donations on heroin.
Officers said public donations were making the problem worse by encouraging begging and, indirectly, drug taking. Superintendent Graham Cox, Hove police commander, said: "Give a coin to a beggar in this town and you are financing the drugs trade.
"There is now considerable evidence that drug habits are being sustained purely through voluntary donations from members of the public.
"We can show there is a definite link and while we will do our bit by warning and prosecuting beggars, I am asking the public to help us.
"If people stopped giving handouts in the streets there would be no more begging.
"I would urge people who want to help to give instead to charities and distribution centres for people in need."
The survey among beggars and people sleeping rough was carried out by officers in June.
Police found only one of those questioned was originally from the Brighton and Hove area. The rest came from out of town, mainly London.
Mr Cox said national studies showed that many beggars were not sleeping rough and that their blankets, sleeping bags and dogs were often "props" designed to make them look more in need.
Police observed some beggars being ferried by car to their "pitches" each morning.
Mr Cox said: "Bearing in mind they were talking to police officers a surprisingly high number, 13, admitted they used donations to buy heroin.
"It makes us think many more of them do the same."
Following the survey, police launched a crackdown.
Begging is an offence and officers have been warning, moving on, and cautioning the law-breakers.
Mr Cox said: "If they don't get the message, we will have no hesitation in taking them to court."
He said begging was connected to serious assaults and, in one case, death.
last month beggar David Gibson was jailed for two-and-a-half years for punching and killing John Hart Gould in Hove, after the victim refused to hand over money.
Mr Cox said: "Kind-hearted members of the public are actually encouraging beggars to stay on the streets because there is less incentive for them to seek proper help, which is available.
"Please do not give to them."
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