Best comeback I've heard to similar screech - "No, I'm his mum actually!"The next thing I know it's some guy .... - Jesus F***ing Christ!

I bear in mind your helpful suggestions. I like the idea of using the left hand signal and possibly the palm facing one, I bear that in mind for the future. I also remember the shouting 

with not much effort at all (it could probably go faster, but I wouldn't feel safe doing more then that, considering the bike has a high centre of gravity).
?In the situation you have described, I would suggest the only hand signal to show you are stopping would be to signal left.
There are three main hand signals that I use:
1. The arm at right angle with pointing finger - To show I am turning.
2. The arm at just about 45 degrees with the palm facing backwards or to a following vehicle - To show that I am either moving out or for the car to wait.
3. The 'patting a large dog slowly' method. Basically waving my arm up and down in varying speeds depending on the imminent danger.
To warn other cyclists that I will stop suddenly (or not) I always shout "Stopping" loudly. It is what we do on the club rides.
I understand that you didnt know this cyclist was behind you (possibly no lights or just came from behind too quickly). He also might not have seen you due to having just one light (I presume) left on your bike.
Without being there we cannot say but at least you were reflective (see what I did there) about the situation.
The only way a driver would hit you for that exact reason is when you are not shoulder checking enough.When I did my cycling proficiency I was taught not to point with my finger when turning lest the driver behind mistake it for, well, pointing at summat. Driver looks for imaginary object, sees nowt, and then proceeds to overtake, collecting me en-route.
how would you want a car ahead of you to slow and stop?mirror signal manouvre in good time, you can't just stick the brakes on and stop
)if a bike behind you was given a start I suggest your stop could have been better
The only way a driver would hit you for that exact reason is when you are not shoulder checking enough.
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Or if the driver is distracted whilst desperately looking for the imaginery object you are pointing at and tweaks you, either as you slow in preparation for the turn or otherwise.
Of course shoulder checks are good, but why give a missleading signal that makes you place greater reliance on them?
I'll stick to the HC recommended ones, after all most drivers were once familiar with the HC.
Which organisation authorises these signs?

Which organisation authorises these signs?![]()
Sorry I have no idea, I was trying to be helpful and just did an Internet search. But the stopping signal is one I use, and have seen used quite a lot when riding with different groups.
These signals are actually taught in drivers' classes here (Ontario) in case you are driving a vehicle without signal lights or dysfunctional signal lights.They are in common use in America, that left arm held up at 90 degrees to turn right confused me when I first rode over there, apparently it is what car drivers used to do when cars didn't have indicators.