Apart from Lane 1. ALL lanes are 'overtaking' lanes.
Very occasionally, you see gantry signs showing the message "Keep to the left, except when overtaking". I can't say it has any effect.
Despite the terms 'slow', 'fast' and 'overtaking' not having been used since the early 60s, they are a long time in the dying. There's even a current advert for Churchill insurance on LBC radio, where a broken-down 'lady' car says "Cars like me should be in the fast lane, and not on the hard shoulder" - to which Churchill, the bulldog, replies "Oh YES!".