I had a motorist cut across a lane (to go into a garage) and cause a crash - and he admitted in court he didn’t look in his mirrors…judge found against me (70:30) cos I was (in his opinion) riding at excessive speed (30mph in 30 zone - in busy traffic)…
thanks Kaos. 
I was referring to Art’s correct procedure of making a turn…
If you follow that procedure Mirror, Signal, Look, Manoevre and do everything… you’ve technically looked twice 
I was trying to be paedantic and make a joke, clearly I failed in my attempts…
Any Judge would rightly have you down as a nobber Nick.
Were you wearing open crotch leathers or a politically incorrect T-shirt at the time?
In a driving exam, failing to stop your manoeuvre when another vehicle or hazard (including a pedestrian) approached whilst performing the manoeuvre, unless they gave way for you to do so, would have failed you.
My instructor hammered it into my head to regularly check for pedestrians and other vehicles from starting to finishing a U-turn or turn in the road and stop if I do, after all, I am creating a hazard to other road users.