They were xenons to begin with - but apparently the Angel eye units have an HID kit. There's lots of stuff they don't show in the program -eg they changed both air filters and not just the one. Mike clarified a lot of stuff on Twitter.
Minus points for them not knowing that shadow chrome is the stock M5 rim colour. But the show definitely highlights that our used car market, especially for //M cars is artificially high. Then again, they have a much bigger stock of cars to choose from, a hideously high fuel price means a 5.0 V8 isn't going to fetch much money, and a 5000 pound M5 will be a ropey thing anyway. Browsing Pistonheads, most of the ones available for that money have been to the moon and back, or have fallen under disreputable owners.