Spies in suits

To those on the inside, it is called The Circuit: a network of former military intelligence, MI6 and Special Branch officers who operate in the shadowy realm of private security and investigation. It is a secret world where operatives, armed with the latest technology, can find out almost anything about anyone - bank details, telephone records, e-mail traffic, criminal records, tax information, mortgage details and even medical records.

As the demand (and fees) for commercial intelligence has increased, membership of The Circuit has changed: investigators are just as likely to be smart-suited former investment bankers, lawyers or journalists.

It is a small interlocking network where much of the work is sub-contracted. Here is a typical scenario: a company is suing a former director and wants to know everything about that individual. Lawyers are consulted who then hire a private intelligence agency. They in turn commission an investigator who will sub-contract the real work to an operative on the cutting edge. They can provide a snapshot of a bank account, telephone records, business reputation, financial status, anything.

There are only between five and 10 people in the country who can directly access bank and telephone records and they are treated like royalty in the industry. "When you go to see them, it is a bit like buying heroin from a dealer or meeting a Hollywood superstar," one operative revealed. "They know they are special and they often have a group of acolytes. They have the power and you have to handle them with care as they can be temperamental. They will deliberately keep you waiting as if they were a tycoon. But some of them don't know their financial value because you can get decent information off them for £200 and then sell it for £1000."

For less controversial practitioners of black arts, the work is done is through contacts. Take access to the Police National Computer (PNC) for criminal records. Tapping into the PNC leaves a fingerprint as every entry is recorded and registered. But private detectives have alternative routes: writing a letter to a friendly police officer with new information about the target gives the officer a legitimate reason to open the file, insert the new data and check the records. Or persuading a police contact in one location to call an officer in the area covering the target of the investigation bypasses the PNC and leaves no trace.

The information is usually provided verbally. If the client wants original documents, a zero is added to the price. "You can get documents if you are prepared to take a risk but it means somebody has to touch the product," said another private detective. "It usually means getting stuff sent to a post office box. In any major city, between two and 10 per cent of boxes belong to private investigators getting documents sent to them." Recruiting an inside human source is still the most valuable asset.

Physical surveillance can be very costly, although the super-rich will pay anything. Prince Jeffri, brother of the Sultan of Brunei, once hired a special team of 16 security operatives just to follow one woman 24 hours a day for two weeks. Insiders say there are three basic price scales: solicitors, corporate and Arab. They argue that the vast majority of their targets are involved in some form of wrongdoing. "We do what the police should be doing," said one. "They often do not have the skills, imagination or resources, so that's where we come in. We often won't take cases on unless the client has a legitimate grievance, rather than just a personal grudge."

A security industry analyst, Equitable Services, predicts that the worldwide private security market will be worth a staggering £150bn by 2010. As demand for these services increase, governments may want to take a closer look. Regulation may be unrealistic because of the secrecy of the work and its practitioners, but some of their controversial tradecraft deserves more scrutiny.

· Mark Hollingsworth is an investigative journalist specialising in security.