London's Met Police has bought a high-grade mobile surveillance system, which can create a fake mobile network, fool your phone into connecting to it, then intercept your communications and track you via IMEI code. It is not messing about.
Once in place, the technology, which is built by UK company Datong and also used by the US Secret Service and the Ministry of Defence, can broadcast its pretend mobile network over a range of 10 square kilometres, allowing the owner to intercept MMS messages and calls from any mobiles that connect to it.
There is one saving grace to consider, though, before you chain yourself to the gates of New Scotland Yard in protest at this possible abuse of your civil liberties -- the system can also be used to put in place an "intelligent denial of service" which would theoretically cut off the signal were a mobile to be used as a trigger for a bomb. [Guardian]