Hello Rupert, welcome on board. I hate to admit this but I failed my test on the u turn three times! I was getting target fixation, every time I saw the kerb on the other side of the road I lost the plot. All the advice I had received from the instructors was to turn my head as far as I could and look down the road.
Anyway I was on the verge of giving up when I decided to try another school. I explained my problem to a lady on the phone. She told me that she had had three people that day who were just like me, and that they were all doing it just fine by the time she had finished with them!
Well I met this lady at the school and out we went. After only ten minutes riding to get the feel for the bike she said ok let's get this turn sorted out. She told me her technique and told me to go for it. With grave misgivings I did so and b***er me I did it! I was then told to do another(gulp)which I did and then another. I could not believe it! Anyway after riding around for about half an hour. She pulled me over in a much narrower road and told me to do a u turn. I said you are joking to which she said no I'm not, go on do it. Three times I did that turn and each time my confidence soared. The day of my test(the next day) I was followed by an examiner in a car. The e stop done, push the bike round and the u turn. No problem!
Later, just like Andy the comms started playing up. I heard about one word in every sentence and was frantically gesticulating at my helmet. I pulled over and the Instructor came storming out of his car at me. He said something about me being deaf but after the silly bu***er changed his batteries it was alright! I think he was a bit embarrassed!
I passed!
How to do the u turn, all the usual advice.
1. Use your back brake to adjust speed
2. Slip the clutch
3. Keep the engine revs up, 'cos it acts as a gyroscope.
4. Lean your body to the left a bit. Not into the turn.
5. Look over your shoulder and pick a target down the road on the opposite side.
Now Polly's secret

(bless her)
You do all of the above except no5.
What you do is turn your head just over your shoulder.
Don't strain your neck!
Pick a target you can see easily, lamp post, coke can, anything you can use as a marker.
Start your turn, either from stationary or rolling and as soon as you see the target it look down the road.
That's it.
Long winded post but I hope it helps you.
Rick