A drug dealer from Renfrew caught at a railway station with £200,000 of sedatives in a suitcase was jailed for 15 months.
James Docherty, 52, was spotted acting suspiciously at Slough railway station by a police community support officer.
The officer, Dan Sykes, searched his bags and found 200,000 blue tablets wrapped in clear plastic bags.
The 93lb (42kg) haul is thought to be the largest ever seized by British Transport Police (BTP) from one train passenger.
Tests revealed the tablets were diazepam, a sedative sometimes sold under the brand-name Valium, with a street re-sale value of £1 each.
The drug can be used as a heroin substitute and is often taken to ease symptoms associated with cocaine abuse. It is only available on prescription in Britain.
Docherty was sentenced to 15 months in prison at Reading Crown Court on Friday, a spokesman for BTP said.
He admitted possessing class C drugs with intent to supply at an earlier hearing.
Mr Sykes, a cycle patrol officer, said he held Docherty after seeing a small number of tablets spill out of the suitcase on a staircase on September 30 last year.
He caught the drugs runner frantically trying to stuff them back inside and when asked what they were, Docherty said: "Temazepam."
Docherty claimed to work in a pharmaceuticals factory and said he was taking them to be destroyed.
Mr Sykes said: "One minute you're handing out information about cycle crime and the next you've stopped a major drug dealer."
Chief Superintendent Mark Newton said: "This incident illustrates just how valuable the work of our PCSOs can be to the wider public."