Twenty-seven dealers were jailed, with five being recommended for deportation, while six other suppliers were given community sentences.

In a four-month crackdown, three officers recruited from other police forces went undercover to target crack and heroin dealers.

The crackdown began as Operation Nullify – an undercover test-purchase sting where evidence was collected by officers using secret video and audio surveillance as they bought heroin, crack cocaine and amphetamine while posing as addicts called Jay, Des and Jimmy.

Once the surveillance and drugs deals were completed as Operation Nullify, between October 2005 and January 2007, Operation Nailed was launched with dozens of arrests being made.

Operation Nailed was the culmination of months of covert investigations involving more than 70 officers, ending in a series of dawn raids launched in February last year.

In all, 57 arrests were made as officers from Northamptonshire Police executed 23 separate search warrants under the Misuse of Drugs Act. While a total of 33 dealers – 32 men and one woman – were arrested, only one suspect is still at large and being hunted by police.

Paul McGuigan, 29, known as Scottish Paul, has a warrant out for his arrest on suspicion of drugs charges and is believed to have fled the country to the continent.

Detective Chief Inspector Jan Meagher, who led the investigation, said the operation was carefully planned, with information passed on by members of the public playing an important part.

She said: "This is part of our effort to tackle the supply of class A drugs, specifically heroin and crack cocaine.

"During the course of our investigations into the people who are supplying those drugs, we uncovered a network of criminality ranging from shoplifting to the organised handling of stolen goods, all linked back to drug supply and abuse.

"Our aim is to disrupt the drug suppliers in Northampton and show people involved in the trade that we can and will take strong action against them."