The Probation Service has noted an increase in the number of offenders using cocaine, while police have discovered it is now the drug of choice for both criminals and non-offenders.

Figures gathered since a change in the law which allows the police to drug test upon arrest show more people arrested by the county force are testing positive for cocaine and crack.

The drug is also proving popular among professional, non-offenders who are approaching addiction services and charities seeking help to deal with their habits.

The latest available figures show there are 3,100 problematic class A users in the county, of whom 1,822 are in treatment.

A growing number of them are abusing cocaine, while fewer are registering heroin use.

Since a change in the law in April 2006, officers are allowed to test for drug use when they make an arrest for a 'trigger' offence such as drugs' possession or shoplifting.

Within the criminal justice system, 2,135 offenders have been screened, with 288 testing positive for cocaine, 161 for opiates and 182 for both.

Andy Pemberton, the assistant chief officer for the Northamptonshire Probation Service, said: "The huge problem we are finding countywide is a systematic decline in heroin use, but a radical increase in cocaine and stimulant use.

"There are more and more users of cocaine and we need to address this group of people and try to do something about it."

While heroin users can be treated with blocking agents or methadone, cocaine abuse is more difficult and expensive to treat.

There are no blocking agents available to counteract its effects. Cocaine addiction also requires more intensive psychological or social intervention.

With a fall in cocaine's price and growing availability, there is now a trend of young professional using on Fridays and Saturdays who are able to fund habits with salaries rather than crime.

Insp Mike Smith, of Northamptonshire Police, said: "Drug testing has made people aware of the extent of cocaine and heroin among people being arrested."