I know what you mean. A few years ago, I saw a similarly ourageous manouvre on the northbound A41 from Watford to the M25 J20 (see Google maps: www.google.co.uk/maps/@51.6926711,-0.4368396,3a,75...n)

A car overtook the second lane of traffic via the (empty) RH turn filer lane just when the lights (straight on) turned green, narrowly avoiding the traffic lights on the other side. They must've been doing at least 50mph at the time. Also personally had a car cut me up at the next juntion at the M25 whereby they decided to turn left from the RH lane, coming from two cars behind me!

Sadly, I'm not surprised at driving behaviour like this these days. Higher levels of vehicle safety is justified by many reckless individuals for their terrible driving standards. These people should be banned for life and imprisioned if they ever get behind the wheel ever again - a lesson to all those idiots who are considering emulating such people that this sort of behaviour isn't tollerated at all.

I wonder whether dashcam footage of these sorts of antics would be sufficient for the Police/CPS to charge the suspect?

I suspect many of us see the occasional demonstration of stupidity, and I would hope that the increasing use of HD dashcams might help to get some of the most deserving cases prosecuted.