Stop and search has been used more frequently in London since 2008
Knife crime has risen in some parts of London despite an increase in the use of police stop and search powers, a criminologist has said.
Professor Marian Fitzgerald said no strong link had been demonstrated between the tactic and a fall in crime.
Knife crime rose by 8.6% in Southwark, south London, despite 9,437 searches being carried out over six months.
Deputy mayor Kit Malthouse said you can "undoubtedly" attribute a London-wide fall in knife crime to stop and search.
Section 60 of the Criminal Justice and Public Order Act enables officers to stop and search anyone in specified areas, without the need for reasonable suspicion.
Since May 2008 the Metropolitan Police force's Operation Blunt 2 has targeted young people suspected of carrying knives in the hope of cutting the number of victims of attacks.
Professor Fitzgerald, at Kent University, analysed Met stop and search statistics from April to October 2009 and concluded there was "no absolute proof that the tactic is of any use".
The statistics showed that during that period 13,247 stop and searches were carried out in Newham, east London, when knife crime fell by 7.7%.
In Islington, north London, 840 searches were carried out and knife crime fell by 24.8%.
But knife crime rose by 8.6% in Southwark despite 9,437 searches being carried out, and it rose by 6% in Waltham Forest, east London, despite 3,123 searches.
Professor Fitzgerald said: "There is not necessarily a strong correlation between the use of this power, very indiscriminately, and falls in knife crime."
She added: "The boroughs that are making the greatest use of Section 60 searches are not necessarily getting a better result than the boroughs that are resisting the pressure and are using it far less."
Professor Fitzgerald said stop and search risked alienating young people and used a "huge" number of police resources.
She said: "It is a very high risk strategy for tackling a problem to which it is not the answer."
But Kit Malthouse, deputy mayor for policing, attributed the use of stop and search to a 7.9% fall in knife crime over the past year.
He said: "I think it's undoubtedly the case that you can link the start of the fall in knife crime across London as a whole from when Operation Blunt 2 started."
Mr Malthouse added: "We have taken 8,000 knives off the street and made 16,000 arrests. That's bound to have had an effect."
A Metropolitan police spokesman declined to comment.