Police carried out a number of warrants at addresses across the Thames Valley and London at about 6am on August 13 last year as part of an operation to clampdown on the supply of the drug known as M-Kat or Meow Meow (mephedrone).
More than 100 officers executed the warrants under The Misuse of Drugs Act at 11 addresses; six in Oxford, one in Cherwell, three in Aylesbury and one in London.
Cash, cars and a quantity of controlled drugs were seized, as part of the investigation called Operation Raise.
Police later established that the offending took place across Aylesbury, Banbury, Oxford, Abingdon and London.
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During the investigation more than 27kgs of mephedrone was seized, which at the time was the largest seizure in the UK of the drug.
Ciaran Macdonagh, 38, of Northampton Street, Oxford, pleaded guilty to one count of conspiring to supply a class B controlled drug, one count of possession of a controlled drug of class A, cocaine, and one count of possession of a controlled drug of class B, cathinone derivative.
Nazar Vishal, 37, of Danvers Road, Oxford, pleaded guilty to three counts of conspiring to supply a class B controlled drug.
James Screeton, 28, of Willes Close, Faringdon, pleaded guilty to two counts of conspiring to supply a class B controlled drug.
Screeton was sentenced to two years and four weeks’ in prison at Oxford Crown Court yesterday (Tuesday).
Macdonagh was sentenced to 16 months’ in prison, suspended for two years, and Vishal was sentenced to five years’ in prison at a previous hearing on August 4.
Jivani Hussain, 52, of Kenilworth Road, Ashford, Surrey, was found not guilty of one count of conspiring to supply a class B controlled drug, following a four day trial.
Investigating officer, Det Insp Bruce Riddell of the Serious and Organised Crime Unit, said: “This was a challenging investigation for the operation team as the crime group were well organised and established.
“Through dedicated work the investigation team identified and evidenced the members, customers and the criminal activity of the group.
“This led to the largest seizure of mephedrone in the United Kingdom when twenty seven kilograms were recovered from a vehicle that was stopped just after Vishal Nazar was seen to load a number of bags into it.
“The use of mephedrone and ketamine are emerging issues within the drugs market and even though they are Class B drugs, then can cause significant health problems to users.
“The sentences show that Thames Valley Police, working together with partners and the support of local communities, will continue to disrupt and dismantle organised crime groups involved in all types of crime.”