The remains of a cannabis cigarette have been found in an ashtray in the first-floor "sin bin" where civil servants go if they want to smoke.
The discovery was made 10 days ago after a woman official sniffed pot in the air. She traced the smell to a recently smoked joint, and informed her superiors.
Personnel chiefs at the ministry, which is known as "Goggs" - Government Offices Great George Street - immediately launched a search, but have so far failed to find the pothead.
The incident has caused hilarity among Treasury civil servants, who are going round joking "We're only here for the crack." However, security staff are not amused. The "sin bin" is only one floor below the office suite of Keith Hellawell, the Government's new "drugs tsar". He has already complained about lax security.
Civil servants are forbidden to take drugs on to government premises, and if caught they would face certain disciplinary action and perhaps even prosecution. The staff have closed ranks and inquiries have got nowhere.
The smokers' room is supposed to be used only by government employees, but much of the routine work, such as internal post, has now gone out to an agency and an outsider could be responsible.
Cannabis campaign, page 11