I think it's the QinetiQ mmWave system they're implementing. Have a look at this and the other info on the QinetiQ site.

The images they show on the site are not particularly revealing, but I've seen others that make no concession to modesty whatsoever. I wouldn't be at all happy about such an intrusion and for other cultures it would be totally heinous. Apparently there are plans to adapt the system to electronically cut and paste the "sensitive" areas (genitals, breasts, etc.) from the personal images and onto virtual mannequins - still visible to the screeners but abstracted from their owners. Strange to think of scanners spending all day looking at thousands of sets of tackle superimposed onto dummies!