Alien8 said:Overtaking is always the way to go.
I disagree, and I'm going to provide an actual example (StreetView) (The Upper Richmond Road from Barnes towards Putney.)
As you can see, the road lanes are quite narrow -- presumably because they added a generous (for London...) cycle lane. There are traffic lights at both junctions (before and after), so there's often slow-moving or stopped traffic in one direction, and faster moving traffic coming the other way.
I always use the cycle lane, which often leads to undertaking the cars. Overtaking leads to conflicts with motorcycles doing the same coming the other way, or insufficient room if there's a lorry coming the other way, or being stuck on the right if the lights turn green.
On the Lower Richmond Road I usually overtake, since there's lots of parked cars and for most of the route a decent amount of space in the centre of the road.
Putney High Street is a place for undertaking cautiously (running speed or less), but overtaking is stupid, with all the buses coming the other way and other vehicles pulling into the centre to go around stuff.