There is no law against it. If you move from a lane to the right to a lane on the left to pass other vehicles, that could be construed as 'dangerous driving' and is advised against in The Highway Code, but is not specifically banned by any law. In fact, where lanes of traffic are moving beside each other and vehicles are staying in lane, lanes to the left will naturally pass lanes to the right depending on flow and blockages. It would be lunacy to brake to prevent yourself passing on the left. In the example a few weeks ago a car in lane one stayed in lane to pass an idiot in lane four. It would have been dangerous stupidity for him to drive out to lane five to pass the idiot then drive back to lane one.