Well I have to say, compared to some of the other unenforceable & unpoliced stupid laws that have been passed; like no talking on mobiles when driving, I think it would be easier to enforce.  Instead of having to "eyeball" a perpetrator in the first place, it would be logged on computer.  Garages that are eligible to carry out MOT's are already vetted by the government and checked randomly as well may I add. So not every mechanic with a spanner, working in your friendly village lockup, would qualify to either do MOT's or collect the Tax on behalf of the DVLA.  As for needing an army to enforce it, the government have just that; to trace and bring to book those guilty of Tax evasion.  So as long as the recovery of otherwise lost revenue, pays for the workforce collecting it; it is deemed worthwhile. I also really don't believe Civil Rights lawyers would do too well, defending people blatantly guilty of evading a legal Tax; with the evidence of such activity on record for all to see.  As for being an infringement of somebody's civil liberties, that's stretching things into the realms of fantasy; you could say paying income tax also qualifies, which of course would be ridiculous.  In their wisdom, the government have decide that the current way of Taxing vehicles; is more cost effective than the old way.  That may be true, as far as running the actual system is concerned, but it certainly isn't true; when the lost revenue is taken into account.  So they're either prepared to lose revenue, so they can cut back on department running costs.........or some whizz kid Civil Servant decided the theory looked good and got it put into practice.........that's where the college of life comes in more handy, than one that hands you a little paper diploma.