Undertaking / filtering on left?

It sometimes feels like I'm the only person in London who does this.

No, I do this, too, and it is recommended behaviour--Cyclecraft or cycle training both teach this.

undertaking is fine in stationary traffic if there is no junctions.

There is still the risk of car doors opening, pedestrians moving between vehicles, and cars can also pull over while stuck in a queue. Unfortunately it's not so simple.

surely if you didn't undertake at all cycling would be just as infuriating as i hear driving is. and it would take me about an hour to commute rather than 30min.

Josh, of course no-one's saying that you shouldn't filter at all. If the queue is very long and there is enough room to filter, then with a little skill filtering is usually possible and not a problem. The various caveats still apply, of course. But: It is often better to pass stationary queues on the offside. It is often better not to filter at all. It is possible to get stuck in queues in which buses or HGVs take up the full width of the carriageway. A lot of inexperienced cyclists then take to filtering dangerously or even cycling along the footway. Neither is a good idea. If you can see that the queue just isn't clearing, get off your bike and walk along the footway, then remount where you have room to continue riding. But more often than you might imagine, patience is the best strategy. People often try to save split seconds because of impatience and it can cause completely unnecessary situations.

But I go faster than all the other people in queue because I'm pulling an awesome trackstand and I'm ready to pounce as soon as the first amber photon graces the back of my eyeballs. So the rules are different for me right?

Of course, if that's how you troll. :)