I am not sure what the device you must drive over scans for (explosives?) but you can indeed find yourself pulled over for a random check - and they do Xray and do other scans on vehicles (including lorries) not just for things like explosives but also for stowaways.
I have no idea the percentage of vehicles that get stopped. In about 10 crossings or so, I've been stopped once - and most of the questioning seemed to be about if I had an LPG conversion (and then wanting to check). I hadn't and I was free to go with minimal delay.
Compared to flying hundreds of times where I've never been stopped once. I either have a very honest face, or actually look so dodgy that they assume I'm innocent as the guilty ones try and look honest!
Thanks for the info, which suggests it's still not a level playing field.
Eurostar is treated like flying, with the single exception as far as I can see that the liquids restrictions do not apply. 100% of people go through a metal detector and 100% of bags are scanned, with a proportion of both undergoing a more detailed search.
Most Tunnel road vehicles, possibly 90%, only receive some sort of underside scan which is almost certainly less rigorous. Equivalent protection would require all occupants to leave the vehicle and pass through detector arches, while the vehicle itself was X-rayed (which would require a very large machine with a very powerful radiation source, which is perhaps why it is used sparingly at present). The stowaway checks are not surprisingly intended to detect people, and I believe they include infra-red cameras and probes to detect excess CO2 from people's breath.
It's possible that there is other technology we don't know about, which subjects vehicles to other checks such as "sniffing" for explosives, but if these can be applied to vehicles then why can't they be applied to people and bags on Eurostar in place of the present arrangements?
