The new DVLA register has helped keep good cars on the road recently and remove hundreds of un-taxed rubbish.
There are still problems with ANPR, and it will take a very big computer to track all 55 million cars all round the country. 
I would guess the idea is for areas of high risk, central london for instance. 
No idea otherwise, and who cares, i havent done anything wrong ?
I quite agree Robbo,  However,  I think I've had a reasonable run so far. Forty years motoring,  Always had a clean licence.  Never had an accident that needed to be reported to the Police.   Then, a couple of months back I get snapped by a camera (36 in a 30).
The road had been a 40 since gods know when.   Then in Feb this year they drop the limit to 30.  No signs to say "watch out" Speed limit reduced.  So I get the offer of  £60 and 3 points or attend a Speed awareness Workshop £70 and no points.  So I of course I take the £70 no points.  
Why did they drop the limit?    
I guess for "safety" so why not advertise it?   
None the less I'm pissed off  it was a bright sunny day on a very wide road with little traffic and no pedestrians.   I don't belive any Police person would have stopped in the circumstances.
The after the course I'm even more PO.  The lecturer addmitted to haveing been done 4 times!!!!  Who the F is he to lecture me about speed awareness?
I just came back from the USA want a pleasue to drive over there.  (Well for a Brit)  No real worries about over doing the speed.    Though I was not the fastest on the freeway.  :-) 
But I had forgotten how pleasant it is to drive the car and not the Speedo.
I could rant on for ages about it.  But I think you get my point.  :-)
T.