Sorry to hear that MDJ, get well soon. You would think by now that people were aware of the phrase "think outside the box", this also applies to drivers of boxes, bunch of jerks.
The Highway Code states the following :-
Manoeuvring. You should be aware of what is behind and to the sides before manoeuvring. Look behind you; use mirrors if they are fitted. When overtaking traffic queues look out for pedestrians crossing between vehicles and vehicles emerging from junctions.
Remember: Observation - Signal -Manoeuvre.
That ia an extract from rules for motorcyclists Paragraph 71. I would therefore assume that they could not prosecute for carrying out a manouvre as described in the Highway Code, although it does not describe it as filtering, I think the operative phrase is when "overtaking traffic queues", which is what you would apperar to have been doing. Have a look at the link
http://www.highwaycode.gov.uk/04.shtml
The Highway code also has rules for drivers, the following is an extract, again from the Highway Code
All mirrors should be used effectively throughout your journey. You should
use your mirrors frequently so that you always know what is behind and to each side of you
use them in good time before you signal or change direction or speed
be aware that mirrors do not cover all areas and there will be blind spots. You will need to look round and check.
Remember: Mirrors - Signal - Manoeuvre
Rule 137 from the Highway code, it also has graphics relating specifically to Motorcyclists, although this relates to moving off, the same should relate to turning, as it states above. Have a look at the link
http://www.highwaycode.gov.uk/14.shtml#135
I was under the impression that the Highway code also formed part of the law, or at least part of the armoury for prosecution under the Road Traffic Laws. It used to as you could be held partly liable for an accident in the previous Highway Code, 1st published around 4 years ago, if you were not wearing a white helmet. I think the MAG + other action groups protested and got the wording changed to the current "white or brightly coloured helmet"
I'm sure someone will tell me it's boll*cks.
Slow in, slow out. Ohh err missus, now with added G-Force carbon fibre race cans. Sounds like a Spitfire.