In many places, the existing layout of roads and buildings means that there is simply not enough space to provide segregated cycle lanes without adversely impacting other users.
Boris Johnson, 23rd February 2011, in answer to question from John Biggs regarding segregated cycle lanes.
Here is a small selection of some London streets, for your perusal.
St. James’s Street.
Tottenham Court Road.
As you can see quite clearly, there really isn’t any point asking for segregated cycle provision in London. There just isn’t enough space.