Absolute nonsense, I'm afraid. You astonishingly state that as long as you indicate, this absolves you from any responsibility, but that is wholly wrong. .

Your use of the word "lawfully" doesn't add anything, and only serves to confuse the issue.

However, and whilst the Highway Code is not "the law", it can be pointed to (and very often is) in support of allegations of negligence, as in, we are all supposed to know it, and comply with it.

On this specific question (with the most relevant bits highlighted) it clearly statesTurning right
179 Well before you turn right you should
* use your mirrors to make sure you know the position and movement of traffic behind you
...

180 Wait until there is a safe gap between you and any oncoming vehicle. Watch out for cyclists, motorcyclists, pedestrians and other road users. Check your mirrors and blind spot again to make sure you are not being overtaken, then make the turn.'"

Can I just throw three pennoth in ?

Humans have a field of vision that is ALMOST 180 degrees, get someone to test yours, its actually quite surprising what you can see to the side of you, I already know what both of my eyes are like for field of vision because I have it tested by my doctor every six months, but a simple test such as getting someone to approach from behind and then holding your hand up when you can see then should surprise you.

Further to that, your vision is also alerted more by moving objects, its an animal instinct sort of thing.

So, a moped approaching your car from behind won't be visible to you yet, but if you turn your head even just slightly then your 180 degree field should pick them up easily, especially if they are deviating from a static location in relation to your eye, in other words they are pulling out to overtake and moving across you field of vision.

What we really need is an almost 360 degree field like some birds do.