Several hundred crack dealers have access to guns - including automatic weapons - Scotland Yard revealed yesterday as it warned that drug-dealing and associated violence was on the increase.

Last year there were at least 10 murders and 20 attempted murders linked directly to the crack trade in London. In the first five months of this year there were three murders and 12 attempted murders.

Commander John Grieve, head of the Met's year-old Drugs Related Violence Intelligence Unit (DRVIU), which collates information from the eight London police areas, said: 'As the market for drugs increases we are seeing an increase in the use of violence and firearms.

Where drugs are concerned, guns are almost always associated with crack dealing. 'There are several hundred persons involved in the crack trade that have access to weaponry and that includes automatic weaponry, said David Veness, Scotland Yard's Assistant Commissioner of Specialist Operations.

During a 39-day period this year there were 470 street incidents involving firearms. The police have adopted a system for collating firearms incidents first pioneered by Greater Manchester police. Every firearms incident is recorded whether or not an offence can be proved. This includes incidents when residents hear shots or empty cartridges are found.

Detective Superintendent Roy Clark, responsible for the day-to-day running of the intelligence unit, and for the handling of informants, said 40 guns were taken out of service in one operation. An average of two incidents of shots being fired per day in London had been recorded.

The police admitted they were having to 'run faster in order to maintain equilibrium over drugs. Using informants had helped them make 1,984 arrests for dealing in the past year. Many of the crack dealers had drifted to Britain from the United States.

At the core of the Met's battle against crack is the central DRVIU computer. Installed last November, it holds information gathered from more than 20 major investigations into crack-related murders.

There are a total of 31 packages of data, said Commander Grieve.

'The DRVIU contains three quarters of a million pieces of jigsaw puzzle. More than 100 bits of this puzzle are picked out per day by police working in the areas. This is a measure of its success.