In the UK do trains ride on the left side as well?

In my experience, on a normal double-tracked railway in Britain the trains always run on the left-hand track, following the custom observed on the highways.

Trains travel on the left hand track (typically) in any two track system. With the lines designated Down (travelling away from London) and Up (travelling towards london).

In four track sections can either be set as a pair of Fast/Slow lines with trains running on alternate directions on each track or as a pair of Up and Down lines obeying the two track driving on the left scenario.