In the wake of the London bombings of 7 July 2005, this jargon term of the law enforcement and security agencies had some circulation in the British press, variously as two words, hyphenated, or as one word. It refers to a person with no criminal record or evidence of actual or potential wrongdoing, who is able to move freely without being flagged as suspicious.
It isn’t limited to terrorism; the word appeared in the British press the year before in reports that the police were concerned that “clean skin” football supporters, with no previous history of violence, would be able to travel to Euro 2004 matches without attracting attention and cause trouble. The earliest examples I know of date from 2001 and refer to an IRA bombing alert in London, including this from the Evening Standard: “Detectives are faced with the difficulty that the terrorists are thought to be ‘clean-skins’ — members not known to the security services who have been recruited since the ceasefire. They usually hold responsible jobs and keep a low profile until they are activated to carry out an attack.”
The word has a long history in Australia. These days, it refers to unlabelled bottles of wine, usually sold by a winery in bulk to a merchant specialising in such goods. The winery is thereby able to dispose of excess stock while keeping the price of its branded output high. The wine merchant then sells the wine on with generic labels attached. But the term is much older. The Australian National Dictionary has examples from 1881 in the sense of an unbranded animal and from 1907 for a person with no criminal record, which appears to be police jargon of the period. Might the intelligence term have come from this? It seems likely.
The paucity of knowledge the intelligence community has about the precise extremist threat is shown by the fact that the four men behind the London bombings have been described as “cleanskins” — people not identified as posing a severe danger.
Guardian, 20 Jul. 2005
The three identified men are regarded as “cleanskins” in that they were not known as potential terrorists. Sources said there had been no intelligence that such a gang was about to attack.
Daily Telegraph, 13 Jul. 2005