The number of Class A drug dealers being arrested in London has fallen by 19% over the last three years.
London has the most number of hard drug users
The London Assembly's Lib Dems said the figures were worrying as the Met said downgrading of cannabis last year would give it more time to pursue hard drugs.
But the force said it was concentrating on "higher tier" dealers adding that while arrests were down seizures of class A drugs had increased.
The latest British Crime Survey shows London has the most hard drug users.
The figures show that in 2001 there were 2,384 people arrested for the supply, or intent to supply, Class A drugs such as heroin and cocaine. By 2004, this had fallen to 1,932.
LONDON DRUG USE
The latest figures from the British Crime Survey shows that London has the highest number of hard drug takers in the country, with more than one in 20 people having taken a Class A drug in the last year
The Met Police estimate that in the first five months following the reclassification of cannabis to a Class C drug in January 2003, it saved police 14,620 hours of red tape.
London Assembly Liberal Democrat policing spokesperson, Graham Tope, said: "These new figures are deeply worrying.
"When cannabis was downgraded by the Home Office, ministers promised that the extra time officers would have would mean that they could tackle hard drug dealers. This is clearly not happening."
Disrupting criminal networks
But a statement from the Met said: "The Met now concentrates through a National Intelligence Model on higher tier dealers.
"In support of our efforts to achieve this, we work with other agencies including the National Crime Squad and our recently created Middle Market team consisting of police officers and customs officers working jointly to tackle serious offenders.
"Therefore while there may be a reduction in numbers of arrests, actual seizures of class A drugs have increased.
"We continue to seek opportunities to reduce harm through dismantling and disrupting criminal networks intent on dealing in illicit drugs."