The UK Border Agency (who do the tracking) tell us proudly:
"The e-Borders scheme has already screened over 82m passengers travelling to Britain, leading to more than 2,900 arrests, for crimes including murder, drug dealing and sex offences. e-borders helps the police catch criminals attempt to escape justice."
So, 35 arrests per million passengers screened. It would be interesting to know what proportion of those arrests were for serious crimes. Is this a good value security investment at an estimated £1.2bn cost over the next decade, even aside from the privacy impact?