Sherlock may have finished its wildly popular BBC run nearly three years ago, but private detectives are back in the spotlight. Credit Suisse hired investigators to shadow a former executive, and the Dechert partner Neil Gerrard is suing Diligence International for allegedly spying on his family holiday in the Caribbean.

Like Benedict Cumberbatch, these cases can set pulses racing, but they hardly reflect the day-to-day reality of what most reputable private investigators, or “business intelligence” services, as some prefer to be called, actually do for law firms.

Although there is no professional code of practice in the field, most law firms are now explicit in their letters of appointment to investigators about how they should behave.

Alex Carruthers commented: “The use of private investigators can be a very tricky area. Clients are often very keen to get the dirt on their ex, but you often have to query the forensic benefit of such reports and the damage that may be done to the client when it is revealed that they spied on their spouse.

“A report from a private investigator can, on rare occasions, be a killer blow in litigation.

“Unfortunately, more often than not, they are of little value and can be a self-inflicted wound showing the desire of one party to spy on the other.”

Read Alex’s comments in The Times.