Commercial tyres normally have stiffer side walls to carry th eadditional weight , this can make them prone to breaking away early compared to cars tyres . Not sure how the Police would view them as there's something in the regs to the effect " suitable for use " . I know they'd get upset about car tyres on vans but don't know about the other way round?

You can get 175 x 16 from here

http://www.tyre-finder.co.uk/stocklist.htm

 

As Kev says van tyres are usually 6 or 8 ply