Basically, it's cos the population in the world has pretty much doubled since the 1960s, and London is one of the premiere global metropolitan areas with good economic prospects.
Thanks Alfie. I was wondering if maybe there had been an accident somewhere on the south circular, or traffic lights gone out of kilter, or roadworks or a burst watermain. But instead, I'll just blame all exceptionally bad traffic jams in future on world population growth and be pleased about our economic prospects.
I see you're new here and sorry if my reply is a tad harsh - but previously, users on this forum have actually spotted things like traffic light timings going wrong which has then been notified to TfL and rectified.