Police officers in New York are "manufacturing" criminal offenses by forcing people with small amounts of marijuana to reveal their drugs, according to a survey by public defenders.

Nearly half of New Yorkers picked up for small amounts of marijuana possession in recent months were not displaying the drug before they were stopped, the study shows, despite an order by New York police chief Ray Kelly that officers should not charge people in such circumstances.

The revelations will fuel criticisms of the NYPD's controversial "stop and frisk" policy, which opponents say is criminalising a generation of young people from ethnic minorities and leading to tensions between police and the public.

Scott Levy, an attorney at the Bronx Defenders, the legal and advocacy organization that led the survey, said: "This is clearly an illegal practice. And the fact that it hasn't stopped since Commissioner Kelly issued his memo, suggests there is a deep disconnect between what happens on the street and what the top brass in the NYPD are saying happens."

Under New York law, possession of 25g or less of marijuana is only a misdemeanor offense, a violation that brings a $100 fine. Only when the drugs are in public view are the police permitted to make an arrest for drug possession.

In September last year, Kelly issued an order to officers not to arrest people caught with small amounts of marijuana. But the number of those arrested increased after the order was made.

In all, about 50,000 people were arrested in 2011 for marijuana possession; some 30,000 of these came after police stops.

In August there were 2,486 arrests after police stops. In October – after the Kelly order – the NYPD arrested 2,661 people on the same charge. That number dipped slightly in November and December, but was still higher than the same months in previous years.

Until now, no one has been able to tell how many of those arrested may have occurred only after a police officer compelled a suspect to pull the drugs out of his or her pocket, which gave them cause for arrest.

To get more detailed data, the Bronx Defenders teamed up with attorneys from the law firm Cleary, Gottlieb, Steen and Hamilton to review police records and personal accounts from 517 people arrested for marijuana possession in the borough in the months before and after the Kelly order.

According to the survey, the percentage of illegal stop-and-frisks increased from 31% before the order to 44% after the order. Similarly, the percentage of manufactured misdemeanors increased from 33% to 44%.

One in three respondents said police had forced them to take the marijuana out of pockets or from under clothes and produce it into public view.

The NYPD did not respond to a request for comment. In the past, it has vigorously defended its policies, arguing that stop and frisks save lives.

But members of communities impacted by stop and frisks disagree, arguing that the policy has resulted in a form of institutionalized degradation that disproportionately impacts African American and Latino youth. They say the tactic leads to harassment and erodes trust between police and the public.

Darnell, who lives in the South Bronx who and requested his last name not be used, was stopped by the NYPD as he was crossing 170th and Valentine streets last October. He said two officers patted him down but stopped short of searching him in public. Instead, they took Darnell back to the precinct and asked him to remove his pants and underwear.

"They went through everything, and finally found about $20 of marijuana in my hat," Darnell said. "They didn't give me no reason for stopping me in the first place." Darnell was held for 12 hours in the precinct and charged with a misdemeanor.

Vinci, another Bronx resident, tells of a more recent interaction with the NYPD the night before the 2012 Super Bowl. "I was coming out of the store and the police stopped me," Vinci said. "I felt real awful you know, it was in front of everyone and I hadn't done anything wrong."

In Vinci's case the officers allegedly searched him on the street and took a small amount of marijuana from inside his pants. Vinci was locked up for 38 hours and released just in time to watch the final minutes of the game.

"It was a distressing experience," he said. "Makes you realize it can happen any time any place."

NYPD data on all stop-and-frisks conducted in 2011 reveals officers suspected just over half of the nearly 684,000 people stopped had drugs on them, and ended up arresting about one in 10 on that count.

In some instances police specified they could smell marijuana or someone was actually smoking it in public. Other reasons police stopped people who they subsequently arrested for marijuana were "furtive movements", "suspicious bulges", "being in a high crime area" and "other".

Community activists have increasingly pushed back against the stop-and-frisk policy with public acts of civil disobedience. Beginning in October, a group calling itself the Stop Mass Incarceration Network launched a series of actions throughout the city with the support of Occupy Wall Street protesters.

Activists willfully subjected themselves to arrest outside a number of NYPD precincts in some of the most heavily impacted neighborhoods in the five boroughs.

Legal experts and criminal justice scholars have claimed that stop-and-frisks – and the drug arrests that often result from them – routinely lead to fourth amendment violations and serve as pipeline for the nation's bloated prison system.

Over the course of the last five years the NYPD has been named in three federal lawsuits over its application of stop-and-frisk practices, with one lawsuit filed as recently as this week.

"If the Kelly order had worked, if his directive had remotely worked," said Levy, "these types of unconstitutional arrests just shouldn't still be happening so frequently."

Gideon Oliver, president of the New York City chapter of the National Lawyers Guild, said he was not surprised to learn the commissioner's directive had not been followed.

He said drug possession charges can have a profoundly negative impact on the lives of those who receive them and the communities they reside in.

"It has tremendous collateral social impacts," he said.

Alice Brennan is a reporter with the New York World, an accountability journalism project covering city and state government