Transport for London
http://www.tfl.gov.uk/roadusers/redroutes/963.aspx

Bus lanes

bus-lane-car Bus lanes aren't just for buses. Taxis, motorcyclists and cyclists can use them most of the time too.

You can drive in bus lanes at certain times. Most vehicles must not use bus lanes during the times they're operational - you'll see this information on a signpost before the lane starts and usually intermittently along the lane.

If no sign is visible, assume that the bus lane is operational 24 hours a day.
When can I enter a bus lane?

During non operational times. The times of operation are indicated on the sign
If you want to turn left within 20 metres of the junction - an arrow or a dotted white line will indicate if this is allowed

If avoiding road works or emergency vehicles

Who can use bus lanes?

Motorcycles (without side cars)
Mopeds
Scooters
Tricycles (non-motorised, motorised under 450kg, not with side cars)
Bicycles
London licensed Taxis
Dial a Ride
Buses which have a minimum of 10 seats (including the driver)

Read the bus lane signs to find out who can use it and when. Some signs may display the word "local" indicating that only local bus services can use the bus lane.
Local Authority roads

These are identified by yellow lines. Bus lanes along these roads may have different rules. Check the signs to see if you can use these bus lanes.
We may issue a £130 penalty charge notice

If you use the bus lane during operational hours. The times of operation are indicated on the sign.