Scotland Yard claimed a significant breakthrough in its battle against street robbery yesterday as figures showed offences had fallen by 31 per cent since the start of the year.

Sir John Stevens, Commissioner of the Metropolitan Police, said the force owed its success to rapid response traffic police who were adept at high-speed pursuits.

But the police claims prompted warnings against complacency, with commentators pointing out that the number of street robberies in the first seven months of this year was greater than for the same period in 2001.

The Metropolitan Police has been given an ultimatum by David Blunkett, the Home Secretary, to reduce street robbery by September or face his direct intervention.

The force released figures yesterday showing that the number of street robbery offences in the capital fell from 224 a day in January to 154 a day last month.

Sir John said: "We are delighted. In December, we identified that the figures were beginning to go through the roof and decided there was a challenge we had to address.

"The key was diverting traffic officers experienced at high-speed driving into street crime to improve the way we responded immediately after a robbery."

Street crime reached a high of 7,010 offences in October last year. Last month, police dealt with 4,786 cases.

In February this year, the Met launched Operation Safer Streets, which diverted 250 traffic officers into fighting street crime. Similar operations have been established in nine other forces across England and Wales.

Richard Barnes, a Conservative member of the Greater London Authority, said it was too early to claim success in tackling the problem and said "a cautionary note" had to be sounded.

Mr Barnes said: "There has still been a greater volume of street crime committed so far this year than was committed in the first seven months last year. Street crime is up by 6 per cent since last year. This is no time to get complacent."

Further inroads into street crime in London are being made by a squad of police officers and traffic wardens that responds to offences committed on buses and in minicabs.

The unit, set up by the Mayor of London, Ken Livingstone, made 240 arrests in its first two months and is being expanded from four bus routes to 26 by March next year.

Arrests include 19 for theft, 10 for drugs offences, nine for assault and seven for carrying an offensive weapon.