Book extract Headspace is Reg contributor Amber Marks's exploration of how the state and private sectors are trying to exploit the science of smell to watch and control citizens.

Over the coming weeks, we will be publishing exclusive extracts from the book, which is published by Virgin Books and available here.

Today we present Chapter 5, "Hijacking The Yeast". Marks is attending a Ministry of Defence conference covering the security applications of olfaction.

The morning of the conference arrived, and I was surprised to sleep through my alarm. I woke up with a jolt in bright sunlight. I hurriedly showered and pulled on black stockings, designer long skirt, black top, black Gucci suit jacket, black leather stilettos and scrambled around for a black handbag. Instead I found a fluffy orange and green bag and a variety of 1970s brown leather bags. I grabbed one, reassuring myself that 1970s items no longer represented Peace or Love but simply Fashion. I glanced in the mirror and pulled my hair back extra tightly, pleased with how stern I looked. I sprayed on some Dolce & Gabbana to complete the effect.

Steve Tapper, a young stocky man with a crew-cut, was next to take the stage. He was studying canine detection in the United States. He opened with a reference to Aristotle, who had apparently said that smell was at the heart of perception. Tapper was concerned by the lack of peer-reviewed publications on the scientific validity of canine detection. Legal challenges to the use of dogs in the US suggested that the police might not be able to rely solely on the reputation of the dog's nose in the future. Judges and juries were starting to ask for scientific proof of a dog's ability to detect and identify specific scents. A lot of work needed to be done; the studies he had carried out had revealed a number of flaws in canine detection.

The United States was attempting to build up a database of human scents. I wondered if perhaps the Americans had the Stasi samples that went missing at the end of their regime. Scientists involved in Tapper's research felt confident that each individual had a particular scent that remained constant over time, regardless of diet or environmental factors. Scents had been collected from the armpits of volunteers. It sounded similar to the means employed to get the DNA database off the ground in the UK: armies of ill-informed volunteers.

The first impediment to the accuracy of scent as a form of identification was that the gauzes used to sample the scent were already impregnated with their own scents, ones shared by some humans. It had not yet been possible to produce an analytically clean medium to impregnate with a scent.

I could see why this might be an impediment.

"Ironically," he concluded, the gauzes used by the FBI, manufactured by the family friendly Johnson & Johnson company, were the most heavily contaminated gauzes. The second impediment was the absence of an agreed unit of measurement. Olfaction lacked a scientific language. He referred us to the website of the Scientific Working Group on Dog and Orthogonal Detection Guidelines. They were working on this problem.

Someone on the front row sneezed. "Bless you," a red-haired and voluptuous American woman called out across the room.

It was my turn to speak.

"The most important concept we need to understand in order to grasp the potential human rights implications of an expansion in olfactory surveillance is the right to privacy."

"The right to privacy has been said to be at the heart of liberty in the modern state. The right to privacy implies that in the absence of compelling justification, we should all be free to move about without fear of being systematically observed by agents of the state. In accordance with the right to privacy, the law requires the police to have reasonable grounds to believe that a crime has been committed by a person before searching them. Until relatively recently, the police had to physically search a person's pockets or houses to find out what was inside of them. This is no longer the case.

"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.

Get more information and buy Headspace here

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