Gurjaipal Dhillon isdue to be sentenced on July 15. (Representational)

An Indian-origin man in the UK has been found guilty of being part of a criminal gang believed to be one of the world's most prolific smugglers of anabolic steroids.

Gurjaipal Dhillon acted as a fixer for the group, arranging dozens of unlicensed shipments of drugs from India into Europe, according to Britain's National Crime Agency (NCA) which led the investigation into the gang.

The 65-year-old from Southall in west London faces years in jail after he was found guilty of conspiring to import a Class C drug following a six-week trial at the Old Bailey court in London on Wednesday.

He, alongside Mumbai-based Danish national Jacob Sporon-Fiedler who has earlier pleaded guilty, is due to be sentenced on July 15.

"Gurjaipal Dhillon was part of a conspiracy to illegally import huge amounts of anabolic steroids into the UK on an unprecedented scale. His role in that conspiracy was a crucial one, essentially organising the transport for the drugs and enabling them to be shipped to the UK," said Rob Burgess, NCA regional head of investigations.

"We believe this organised criminal group to be the most prolific of its kind ever uncovered, probably the biggest global players in the illicit anabolic steroid market," he said.

National Crime Agency officers believe the group, headed by Jacob Sporon-Fiedler as the CEO of an India-based pharmaceutical firm, have smuggled at least 42 tonnes of illicit anabolic steroids into the UK.

The NCA investigation began in 2014, following a seizure of around 300 kilos of the Class C regulated drug by Border Force officers at Heathrow Airport. The load was destined for an address in Belfast, Northern Ireland.

Following that, NCA investigators began to piece together the movement of dozens of unlicensed shipments of drugs, many of which were organised by Dhillon.

Rob Burgess added: "They had the ability to move tonnes of anabolic steroids into Europe where they would be sold on the black market, pocketing millions of pounds in profit. These drugs were completely unregulated and not subject to the usual stringent checks, therefore they posed potentially major health risks to those who used them.

"At the heart of the network lay Jacob Sporon-Fiedler, the CEO of the pharmaceutical company manufacturing the product itself."

NCA said that while its investigation had identified importations totalling almost 42 tonnes of illegal steroids, it is likely the gang were responsible for far more.

Intelligence supplied by the NCA has led to further seizures and criminal investigations by law enforcement partners across Europe.

Nick Jariwalla, Director Border Force Heathrow Airport, said: "Border Force works hard to keep individuals and communities safe from the illegal importation of illicit drugs like these. By making seizures Border Force not only disrupts the supply chains, but, as was the case here, can also provide the crucial first evidence that helps bring those responsible to justice."

The illegally imported drugs - made by Sporon-Fiedler's pharmaceutical company in India - were shipped using Dhillon's contacts.

Once in the UK they would be distributed by Nathan Selcon, 44, to be sold to body builders and fitness fanatics on the black market. Selcon has also pleaded guilty to the crime earlier and is due to be sentenced next month.