Michael Smith, who runs Word 4 Weapons, was speaking after a major new police offensive to get knives off the streets was launched.
New figures released last month showed knife crime went up by 9% last year.
There have already been eight murders this year caused by knives in London.
The week long police crackdown includes increased stop and searches, raids on gang hideouts and other places with knives and other weapons, and performing test purchases in collaboration with Trading Standards to find out which shops are selling knives to underage buyers.
Michael Smith said that increased funding was also needed for education programmes so that young people were not only learning from their peers who may be carrying weapons.
He told Premier's News Hour: "In order to get the community to work or to get crime under control - whatever crime it is - you must have the involvement and the cooperation of the community.
"So it's not just a police matter - it's a community matter.
"There needs to be a cessation of the cutting of funds to do their work, and the cutting of police numbers. That has to stop.
"If you can't provide a proper police service to police the community you will not have enough people out there to do what needs to be done.
"People will lose trust because police are unable to carry out their duties effectively and efficiently, but the more you cut the numbers it becomes more difficult to say 'we can trust the police to do this or that'.
"What you're left with is people taking the law into their own hands."
In a statement to Premier, Minister for Policing, Fire, Criminal Justice and Victims Mike Penning said: "The Government has made reducing violence, including knife crime, a priority and continues to work closely with the police and other organisations to tackle the drivers of these crimes.
"But we know there is more to do. Last year, we legislated to ensure that those convicted of carrying a knife more than once are automatically sent to prison and we are reviewing our measures on knife crime further - including supporting co-ordinated police action and discussing with retailers what more they can do.
Listen to Premier's Hannah Tooley speaking to Michael Smith on the News Hour: