Fair enough, IMHO. Vehicle has been pulled with a serious defect so make sure it's tip top before it's back on the road. You need an MOT every year anyway. Shouldn't be that onerous.
Kevin
There goes my exhaust then. Seem like too many chiefs etc. Can't take a poo without some anorak who's attended a course, read a book been given a hi vis telling you how to wipe. 
The VOSA check is just like the many 'Mermaid' stops that you, as an HGV (or LGV in newspeak) have undertaken. Its basically a roadside MOT. If the fella failed the roadside test then, ergo, he would have failed if he had taken the car for a full blown test that day.
We all know an MOT is barely worth the paper its written on but, if it were not for the testing, then there would be a fair old prportion of scrappy wrecks driving around now, just like there used to be in the days of the escort and Cortina.
And there were a fair few rustbuckets of other makes making the rounds then as well!!