Five men will be sentenced next month for their part in a plot which saw heroin worth more than £9 million smuggled into the UK in bottles of baby powder sent through the post.

A jury yesterday reached final verdicts at the end of a trial lasting more than ten weeks and during which the prosecution described how parcels were originally sent from post offices in Bradford to Pakistan using a recorded or tracked service.

Once they arrived, accomplices replaced the contents with plastic bottles of baby powder manufactured in Thailand which they had partially emptied, inserting packages of heroin instead inside. The parcels were then sent back to addresses in Hull and Manchester marked “undelivered – return to sender” or similar words, said Jonathan Sandiford, prosecuting.

The jury at Leeds Crown Court heard the smuggling came to light in 2011 after staff at a Royal Mail delivery office in Hull became suspicious at the number of such parcels arriving there.

Five were intercepted that March and found to contain an average of 1.9 kilogrammes of heroin. The overall total of 9.460 kilogrammes had a street value of £473,000.

Police identified that a further 94 packages had already been delivered, which meant a street value of £8.93 million. They had been posted originally from 12 post offices in Bradford.

After the Hull operation was detected, further heroin was imported through addresses in Manchester where authorities intercepted a parcel of lengths of cloth hiding food containers holding a further seven kilogrammes of heroin.

Mr Sandiford said the main player and beneficiary of the conspiracies was Khalid Mahmood, who spent thousands of pounds on work at his home in Bradford, funded by proceeds from the drug trade. He adopted a “hands-off approach” relying on others to take the risks, especially his “right-hand man” Faisal Khan.

On September 29, 2011, when Khan was arrested, he was in possession of more than £110,000 in cash, most of which was abnormally contaminated with heroin and Paracetamol, often used as a cutting agent to bulk drugs out and increase profits.

Yasser Uddin was a postman who was familiar with the Royal Mail system.He was in contact with two men in Hull, Paul Cahalin and Alan Riley, who arranged the drop addresses for the packages used in that city and between them transported them to Bradford on arrival. They have already been jailed.

When Uddin’s home was searched police found over £13,500 in cash as well as watches worth more than £5,000.

Telephone links were also shown between Cahalin and Usman Bari, who ran Mamma Mia takeway in Hull and was a long-term associate of Mahmood. Fiaz Ahmed, from Oldham, was Uddin’s brother-in-law and was involved in dealing with the heroin once it arrived in the UK.

The jury unanimously found Mahmood, 30, of Low Lane, Clayton, Bradford and Bari, 33, of Middleton Court, Hull, guilty yesterday of conspiracy to import class A drugs, conspiracy to supply and conspiracy to launder the proceeds.

Faisal Khan, 30 of Burnett Avenue, Marshfields, Bradford, Yasser Uddin, 31 of Clifton Villas, Manningham, Bradford, and Fiaz Ahmed, 31 of Cambridge Street, Oldham, were each found guilty of the same offences last week, when another man was cleared of conspiracy to supply and conspiracy to launder proceeds. Two other men were acquitted on other charges.