Nope, correct procedure as per the HC is to remain in your lane. No issues at all with passing slower traffic on the left. Rule 268 of the HC:
"Do not overtake on the left or move to a lane on your left to overtake. In congested conditions, where adjacent lanes of traffic are moving at similar speeds, traffic in left-hand lanes may sometimes be moving faster than traffic to the right. In these conditions you may keep up with the traffic in your lane even if this means passing traffic in the lane to your right. Do not weave in and out of lanes to overtake."
As long as you don't change lanes to undertake, it's perfectly fine.