Watch out for douchebags trying to clothes line you

I'm not so sure if you can call this "very very rare", you might think it's rare just because you got used to hear these stories, but actually there is a problem if you start thinking about how many people you know who can tell similar stories (including myself).

None, would be the short answer. None of my cycling friends or colleagues, as far as I know, have been attacked in the way the OP describes. So who's anecdotal evidence is valid?

In comparison to what?

Being attacked by Morris men wielding courgettes is "very very rare" scumbag kids attacking folk isn't. They've been doing it all over London for ages, to cyclists, pedestrians, whatever.

In comparison to the number of people I know who are faster riders than you?
I wasn't talking about overall violent crime.
The specific kind of attack mentioned in the OP is very very rare. How many miles a week, or a month, or a year, does the membership of LFGSS ride? And how many of those journeys ended in this kind of incident?
This inflated sense of danger amongst some forum members mirrors very closely the inflated sense of risk associated with cycling in general that stops a lot of the general public riding a bike.
There is a risk, it is very small but it's probably worth keeping in mind of you are riding through certain areas. That's all. It's not an epidemic.