Good enough for Mr Bean to drive.
And I remember seeing Top Gear trying to do a lap of their track in one. Didn't end well. 
And speaking of stuff I've seen on Top Gear, both the Ariel Atom & Caterham are also British and road legal, aren't they?
The old Robin Reliant was a scary machine : with very strange drivers : I recall driving on the motorway in my old Land Rover, torrential rain, couldn't see beggar all for spray ; down to 40mph and thinking it was time to slow some more and flying past me comes a Reliant, throwing up a massive bow-wave, looking like it was about to take-off : obviously worked better as a boat than a car...
Caterham, and some other marques, filled a quasi-legal loophole ; they were not actually sold as complete cars, which would mean expensive crash-testing, etc.. they are 'kit-cars', you are supposed to assemble them yourself, thus avoiding legal stuff and also a bunch of taxes : in actuality, you pay 'some-one' to assemble it for you (which is legal too).. its wierd stuff, but that's how Lotus began, Caterham is now fully-owned by Lotus (who are malaysian-owned, I think), which is a bit circular, cos Caterham started by taking over building the Lotus7, after Lotus went upmarket with Elans and the like.
Not sure about Ariel : its a beefed up motorbike with extra wheels, really. There are some small scale outfits like them, but not really established builders as such, more assemblers of various bought-in parts onto self-built chassis : they do build some wild stuff though, the Bobcat (Land-Rover based) is a seriously fast and proficient off-roader, there is another lot who turn old Citroen Dyanes into pre-war Morgan-style three wheelers, and there we are, back to 3-wheelers and Morgans...
