Undertaking / filtering on left?

wife went to London at weekend and saw van driver wanting to turn left with indicator on-had to "park up" and wait while 20 or so (and she's not prone to exaggerate)cylists undertook-some cyclists are not trying to endear themselves to motorists and with so many riding riskily it must be fluke that there are'nt more collisions

That behaviour is standard on my commute. I'm one of the few who will drop back to let vehicles do their thing or slow down/stop to let vehicles emerge from side roads. Most of the time it seems like a waste as everybody else undertakes or overtakes.

Cycle training - so very useful, but I consider myself a commuting newbie of 18 months.