Bus lanes are a sometimes controversial topic, but they are designed to encourage the use of public transport over private cars and being passed by a bus while sitting in traffic suggests they have some value. However, an observant driver will make use of all the available lanes, and obey Rule 264 of the Highway Code which states you should keep left unless overtaking. It may be that many drivers are too lazy or inattentive to notice the signs displaying a bus lane's times of operation, or potentially that the fear of fines for driving in a bus lane discourage them from doing so. On the other hand, while some drivers are reluctant to use them it leaves them clear for good drivers to take advantage of.