Cycle lanes in Britain have two purposes. The main one is safety. By forcing you to stop, get off your bike, and walk, they make you get home later, thus reducing the amount of time you spend in the house, which as we all know is the place most accidents happen.
The second purpose is the message they send out to motorists, letting them know how the road space is shared out. The message sent out is usually in Basque or Etruscan or Linear B because nobody can understand it. But this one, in Lombard St in Battersea, is pretty clear: cyclists, get off the road, and go where you belong, er, on to the pavement.