Is passing traffic on the cars' passenger side ("Undertaking") with a bicycle frowned upon in the UK? Take the example where a bicycle lane is on the road, rather than the pavement. There is a queue of cars waiting at the lights, and the bike lane is clear right up to the lights. If you were to cycle right up to the lights, you would be passing all the queuing cars on the way, on the passenger side (&quot;Undertaking&quot;). Is this an example of &quot;dangerous driving&quot;, or otherwise frowned upon (UK)? What if the cars were moving? What if there wasn't a bike lane, but you were staying to the side of the road so that other cars could overtake you if they wanted?
As the previous answer states, you're perfectly within your rights to continue along the cycle lane in this situation, regardless of any cars to your right.
Some junctions even have advanced stop lines (see rule 178), which are explicitly designed for exactly this purpose: allowing and encouraging bicycles to pass beyond the stopped cars and position themselves in front of other traffic (this is generally preferable, as it makes the cyclists much more visible to drivers).
You should of course still maintain awareness of the traffic (especially if there are large vehicles such as HGVs or buses, which often have significant blind spots), and be prepared to make a quick stop if it appears that a vehicle is about to cross the cycle lane.
But not only is this allowed for bikes, in the specific situation you're asking about - passing traffic which is stopped at a red light - it's also perfectly fine (and indeed expected) for cars to undertake.
See Rule 163 of the highway code:

Rule 163
Overtake only when it is safe and legal to do so. You should:
[...]
stay in your lane if traffic is moving slowly in queues. If the queue on your right is moving more slowly than you are, you may pass on the left
[...]

(my emphasis)
Note also (admittedly now getting some way from the original question) that the points in rule 163 are governed by &quot;You should&quot;, not &quot;You must&quot;. As explained in the Wording of the Highway Code, that indicates advice rather than legal requirements per se (failing to follow the advice can lead to liability in an accident, but isn't prohibited in itself).