The bomb hoaxer whose 999 calls put part of Knaresborough in lockdown for hours last autumn is a convicted drug dealer, The Press can now reveal.

After the jury at York Crown Court returned unanimous verdicts convicting Shamsul Islam of making three bomb hoax calls, the Recorder of York, Judge Stephen Ashurst revealed he is already serving a prison sentence for possessing heroin and cocaine with intent.

Now the 23-year-old faces an extra sentence of up to seven years for the two 999 calls and the one to Crimestoppers he made on October 16 falsely claiming that Islamist fundamentalists were using Paragon Pizza in High Street, Knaresborough, for bomb making and planned to plant a bomb that night.

The jury heard how North Yorkshire Police sent teams of armed officers to the scene, shut off part of the town centre and ordered everyone to stay indoors, including children at a school in the area, arrested the innocent staff at the takeaway and searched them and the premises. The operation, which began mid-afternoon, was so big officers had to be taken away from their work elsewhere in the county and lasted for hours until the all-clear was given after 8pm.

Judge Ashurst told Islam, of Spencer Place, Leeds: "This was an extremely serious series of hoaxes which caused a very considerable degree of distress and risk to other people, not only a high level of fear and embarrassment for the men who were wrongly suspected of taking part in what was never a bomb plot."

He adjourned sentence until December 9, when Islam, already serving eight years in jail for the drug offences and other matters, will be sentenced alongside his brother Habibul, 22, of Spencer Place, who has admitted insurance fraud and perverting the course of justice by giving the police false car documents.

Prosecution barrister Paul Newcombe told York Crown Court the hoaxes were Shamsul Islam's revenge on staff at the takeaway, who didn't back up his lies when he was stopped driving Habibul Islam's car which was insured at the takeaway's address, although both brothers lived in Leeds.

Shamsul Islam, whom the prosecution described as a "pathological liar" pleaded guilty to perverting the course of justice by lying to police when stopped and dangerous driving the day after the hoaxes in a bid to get away from the police. He denied the bomb hoaxes.