Undertaking / filtering on left?

Overtake.

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.

sorry i was reading this thread as "you shouldn't pass stationary vehicles on either side."

understand now.

(: