The least used cycle lane which I've seen is the one that runs along Sydenham from the roundabout at the top of the hill with the junction of Kirkdale to the other end with the junction of Crystal Palace Parade. I have never seen a single cyclist use it, what an absolute waste, of infrastructure and money. Seems some have no common sense and just follow the lead of oh, let's put a cycle lane in, even though no one will use it. Utterly ridiculous. Well done Lewisham Council, who I presume are responsible for it. All it actually does is reduce valuable road space and slow down traffic.
And if the intention is to slow traffic to a snail pace, mission succeeded, if it is to annoy and frustrate other road users and passengers, mission accomplished. Did it save a life or make a difference, no, it's just inconvenient to everyone else.