Not all bus lanes are open to bikers

It looks like not all bus lanes are available to bikers… TFL are advising that you cannot use a bus lane if it does not have a sign with a bike on it.

Lots of bus lanes in London do not have these signs- try Regent Street W1 and all around Wandsworth and South London.

Does anyone know what % of bus lanes (by number or distance?) are open to bikers?