Four men who produced millions of fake Valium pills every day from a backstreet garage have been jailed for a total of 19 years.

Police who raided the drugs factory found 1,676,094 Etizolam pills, which are dubbed the Blue Plague, with a maximum street value of £1.68m.

The gang used a specialist £20,000 pill press to churn out 250,000 tablets an hour in an operation thought to be one of the UK's largest.

Scott McGaw, 33, of Victoria Road in Paisley, and Eric Reid 45, of Blackwood Terrace, Johnstone, were convicted of producing the drug at an address in Paisley between May 26, 2016 and March 1, 2017.

McGaw was jailed for five years while Reid was sentenced to five-and-a-half years in prison.

The pair recruited self taught chemistry expert Harry Ingle, who was jailed for five-and-a-half years, to the make the drug.

His friend Nicholas Conway, who joined the operation in February last year, was sentenced to three years in prison after pleading guilty to being involved in the supply.

The court heard Ingle, 40, from Reading, Berkshire, and Conway, 45, from London, were found at the premises wearing forensic suits which were covered in blue dust.

Initially they claimed they were there as cleaners, but during the trial they admitted their part in the operation.

McGaw was the man who provided the money to set up the operation and Reid the facilitator who rented the premises and organised the delivery of materials from as far afield as China.

Neither McGaw nor Reid gave evidence, but they claimed that they walked away from the operation when Etizolam changed from a "legal high" to an illegal drug in May 2017.

Lord Burns said: "This was production of this drugs on an industrial scale, capable of producing millions of tablets a day and was a major source of what has been described as a flood into the market in Scotland.

"The profit from this vile trade was enormous."

Detective Constable Greig Baxter, a drug specialist with Police Scotland's STOP unit, said: "This was the biggest production of Etizolam I've ever attended.

"I know of no-one who has come across a pill press press operation as large as this in the UK."

He added: "In March 2017 Etizolam was selling for 50p or £1 a pill. We found 1,676,094 tablets on the premises.

"If sold for £1 a tablet this would realise £1,676,000."

He then told prosecutor Jane Farquharson QC : "If they were bought in deals of 1000 pills they would realise £251,400."

The jury was shown a video of the police search of the premises which showed the pill press in operation and also a machine for bagging the pills and another to wash excess dust off them.

Mixing agents were also discovered on the premises.

The whole drug making operation area was covered in thick blue dust.