So what could the MoD learn from the Stasi?

"Some courts have dismissed the argument that a 'sniff' constitutes a search as absurd, on the basis that mere sensory perception cannot infringe the right to privacy because odours emitted from a person are exposed to the plain perception of the public at large. This reasoning ignores the fact that dogs are used precisely because of their supposed ability to detect odours, which are not exposed to the plain perception of the public at large."

"The US Supreme Court has recently recognised the threat to privacy posed by new surveillance techniques in Kyllo v. United States. In that case the police had aimed a thermal-imaging device at the appellant's residence to detect heat emanations associated with high-powered marijuana growing lamps. Based on the thermal-imaging information, police obtained a search warrant for the residence and found marijuana. In the appeal against the resulting conviction, the court held that when the police obtain by sense-enhancing technology any information regarding the interior of the home that could not otherwise have been obtained without physical intrusion into a constitutionally protected area, that constitutes a search and reasonable grounds are required to make that search legal. The court observed that this would assure preservation of that degree of privacy against government that existed when the right to privacy was adopted.

"There are some judges who believe that if constitutional scrutiny is in order for the imager, it is in order for the dog. Some courts have declared that the use of a sniffer dog, without reasonable suspicion to justify it, amounts to an illegal search and that any evidence found as a result of it should be declared inadmissible."

Having dealt with the law on privacy, I briefly discussed the difficulties presented by the use of olfactory evidence.

"Any questions?" the chair asked.

A man in the front row put his hand up.

"Presumably what you are saying about intrusion on privacy and legality applies to a lot of the new technologies we are developing."

His accent was soft and American.

"Probably."

"And are you saying that if we suspect someone is a suicide bomber, we invade his privacy without any prior suspicions, and we find bombs, that we would not then be allowed to rely on the evidence because of the privacy breach?"

"Well, no. In practice, and in those circumstances, that evidence would be permitted despite police having broken the law to obtain it."

Randy shouted out from the back row. "It's not that simple though Amber. If we think someone is carrying a bomb, we don't stop and search the guy, we terminate him."

Extracted from Headspace by Amber Marks, published by Virgin Books at £11.99. Copyright © Amber Marks 2008.

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Amber Marks is a criminal lawyer and freelance writer. She is presently undertaking doctoral research into new surveillance technologies at King's College, London.