Zitat
what the law says is ambiguous by the use of the word "may".
...
"you may need to fit suitable towing mirrors."
I think the ambiguity arises because the law doesn't know what mirrors your car/towing vehicle is already fitted with. The law says only that you must have adequate rear vision. If you already have mirrors that give you this, then you're ok. If not, then you are required to modify your car so as to achieve it. It's the "if/if not" that gives rise to the "may", and therefore the ambiguity.
We could then go on to dicker about what constitutes "adequate", but I'm sure there was a diagram posted here a while back showing sightlines and blindspots, so it's not too difficult to work it out.
For my part, as long as I can see where the Eriba's nearside wheel is relative to the kerb, then I'm ok. No matter how I adjust the RAV's n/s mirror, I can't see it, so, never mind what the law says, I need at least one additional mirror.