[ThatOtherGuy]

What I did hope to discover is was there a reason for the non single file behaviour when roads or traffic would, (in my mind logically), indicate otherwise.

What doesn't help is the UK highway code is fairly open to interpretation the actual wording is: 

Yes there is a logic for not riding single file, its very simple. If you ride single file you almost inherently invite either a "punishment pass" form a driver, or a poorly thought pass.  Riding 2 abreast which is in almost every jurisdiction on the world totally legal. Otherwise how could cyclists pass each other legally? Riding wide or 2 abreast makes you a forethought in a motorists mind rather than an after thought. It forces the motorist to actually take a moment to think about their actions rather than just "slip by" and then when they realise they have made a mistake, they take out the cyclist as the "easy" option rather than have the head on collision from their ill thought maneuver.

You're right, Australian road laws are no better, in fact I enjoy taking on the jack boots if I am ever pulled over. I keep a copy of the road regulations on my phone and force them to elocute exactly what they think they are going to ticket me for, and then read them the law, even happy to take it to court, and then spank them in front of the magistrate which I have done a number of times. That threat alone leaves most of them walking away tail between their legs.

If you hadn't guessed, I am very passionate about road safety, and having achieved changes in road rules in my own country that protect vulnerable road users, I truly despise the ignorant masses who want to be road bullies.