time if the encounter results in release of the suspect.
In brief, it works by using a mobile fingerprint reader and a GPRS connections to compare two index prints against the national fingerprint database. Legislation in the UK permits the holding of all fingerprints taken after arrest.
The database compared against is the national fingerprint database (IDENT1) containing prints of all convicted criminals and those of a whole bunch of other folk that have at some point been arrested and subsequently released. Suspects do not have to comply with the request for their fingerprints since there is no such legislation relating to the period before arrest. However, I imagine that refusing to give your prints is likely to convince the officer that it is worth the risk of arresting you.
So, on the face of it, this looks like an excellent application of fingerprint biometrics for identification and thereby saving police time. Currently, they are only used to identify the occupants of vehicles that have been listed, say, for not being taxed or having been stolen. I expect we will see these mobile units deployed much more widely in the near future for other identification needs in the field.