So this is how those card skimming ATM false fronts work: the device is very simple, made from moulded polystyrene (or similar), engineered to fit one ATM model and spray-painted in a colour close enough to the real thing with all of the appropriate card logos glued on.
The business end of the device (behind the thin polystyrene front) seems to include a card reader for recording stripes (and, presumably storing them in a simple, time-stamped format) but no way of recording PINs. Of course, the scary thing about that last bit of information is that it requires the skimmer to hang around and watch you type in your PIN and then record it (write it down, I suppose), with an approximate time stamp, so that it can be matched up with its stripe later on.
The thing obviously doesn’t have a radio so it looks like the only way to harvest its store of stripes is to recover the false front itself, which, given what happened at Tesco in Radlett yesterday, implies a certain redundancy – they must have a stack of these things in a lock-up somewhere.