Members of a gang has been jailed for a total of nearly 50 years for their involvement in a large-scale drugs operation in central Scotland.

Prosecutors said the sentences marked the culmination of a surveillance investigation into the drugs network, which was based out of a waste disposal company in Shotts, North Lanarkshire, and directed by a convicted murderer from within prison.

The seven men had been convicted of "grave contraventions of the Misuse of Drugs Act", principally over the supply of heroin.

Convicted killer Stephen Nisbet, 40, the "principal figure" in the gang, received the longest sentence - 12 years - at the High Court in Glasgow today.

He had been convicted of three charges, including being concerned in supplying heroin with a potential value of about £1 million.

James Nisbet, 45, who was said to have been involved to a lesser extent than his brother in relation to one of the charges, was sentenced to 10 years behind bars.

Other men who had lesser roles within the gang were jailed for between four and almost eight years for their involvement.

John McMahon, 27, was jailed for seven years and 10 months while 34-year-old David Milne was sentenced to four years' imprisonment.

Robert Borland, 35, Ronald Harrison, 52, and Allan Holland, 38, were locked up for five years each.

Details of the sentences were revealed by the Judicial Office and Crown Office following the hearing.

Passing sentence, judge Lord Armstrong said: "The quantities and values of the various drugs recovered were significant and the manner of their distribution and supply ... indicates that you were all concerned in operations which were organised and planned.

"The courts have repeatedly made clear that anyone who chooses to become involved in the supplying of high-value amounts of controlled drugs, in whatever capacity, must expect to receive a substantial custodial sentence when brought to justice.

"The court must take full and proper account of the widespread harm that is caused by the supply and abuse of controlled drugs."

Speaking after sentencing, Lindsey Miller, procurator fiscal for organised crime and counter-terrorism, said: "A large-scale criminal network that sought to distribute millions of pounds of heroin across central Scotland has now been systematically dismantled.

"The accused kept on attempting to deal heroin even as their couriers and associates were being arrested, even as their drugs were being seized while all the time investigators were building a stronger case against them.

"The combination of painstaking mobile analysis and seven months of surveillance clearly showed the nature of the drug-dealing family business run by the Nisbet brothers, with Stephen Nisbet directing the drug dealing using mobile phones from inside Edinburgh Prison, and his brother James Nisbet ensuring the distribution of the drugs across Scotland from his premises at Platinum Waste Solutions, Shotts.

"Today's sentences act as a warning to criminals in Scotland that police and prosecutors are determined to bring them to justice and Proceeds of Crime actions have now been initiated against two accused to reclaim their illegal profits."