@ Steve' comment:
"by comparison to other motor vehicles they are (per seat) the least efficient users of fuel"
OK, let us make some assumptions from the start. An efficient car, a diesel, will do about 60mpg (probably less around london, but we'll use this), and carry 5 people. This equates to 300 personmiles per gallon. It takes up 1 'unit' of road area.
A regular, petrol car will do about 35mpg, and carry 5 people =>175pmpg @ 1 unit of road area.
An efficient commuter bike will do over 100mpg, normaly over 120mpg around town, and carry 2 people, giving 240pmpg. About 4 could fit in the space of the above car in congestion, so it takes up 1/4 unit of road area.
So far, the diesel is on top in fuel usage, the bike in people per unit road area. However, there is a catch: How many cars do you see full? I don't live in London, but I rarely see a car with more than 2 occupants. I also rarely see a bike with a pillion.
So rejigging, giving the car the benefit of the doubt and taking 2 occupants, and assuming the bike is not carrying a passenger, this comes down to:
Deisel car: 120pmpg, 0.5 units road pp
Petrol car: 70pmpg, 0.5 units road pp
Bike: 120pmpg, 0.25 units road pp
This gives the bike the edge. Do your maths before commenting.
As to "they try to sneak through gaps in traffic", it's called filtering, have a look in the highway code. They have a perfect right to do this. And, if they are allowed to use bus lanes, this won't happen anymore (or at least as much), nor will them getting stuck.
And "They wait for the lights in ASL", do you know how many times I have seen cars do the same? Or wait on hatched areas, park in bus stops, use bus lanes... There are always going to be idiots on the road, or people who don't think the law applies to them (and the vast majority of them, even in proportion to the numbers of a vehicle type on the road, are car drivers).
I do not live or work in London, and do not want to, but these apply to every major city I have worked in.