Sherlock Holmes would cast a cursory glance at the footprints left by a fleeing criminal before calmly announcing that the man would be found at Rotherhithe Docks aboard a Calcutta-bound tea clipper due to leave port on the next tide. And how did he know? Elementary, my dear Watson.

The rolling gait revealed by the angle of the footprint suggested a sailor. The gob of chewing tobacco left within the imprint was of a type to be obtained only in India - and why go there but for the tea trade? And what fool would carry out such a brazen robbery without the assurance of a swift getaway?

Later fictional forays into forensic science tend to be more visceral. Barely an episode of Morse goes by without the famously squeamish detective having to witness some fascinating clue amid the gore of the post-mortem room. The blood-free stuff hasn't had a look in since the days of Agatha Christie.

For most people, forensic science will always be about fictional police work of this sort. Indeed, the origin of the Forensic Science Service was as a part of the Home Office, and it works closely with the 43 English and Welsh police forces. According to its annual report, it took on 97,000 cases last year.

But since becoming an executive agency, the FSS has been diversifying fast. Remember last month's claim that one worker in 10 tested positive for drugs?

That was FSS. Selling services to employers on 'human problems such as drug and alcohol abuse' is now something of a money-spinner.

Though by far the biggest forensic science body, with 800 forensic scientists, FSS is not alone. Information about the wider world of forensic science can be found through the Forensic Science Society, the calling's professional body. These days, it is all far from elementary.