A reluctant commuter, I use Embankment underground station regularly.. The northbound platform on the Northern Line is built on a tight curve and this potential hazard to travellers prompts the recorded message "Mind the Gap" every time a train arrives and the carriage doors slide open. The message is delivered in a brisk patrician voice recorded for London Underground (as it then was0 by the actor Oswald Lawrence in 1969 "MAIND THE GEP" (pause) "MAIND THE `GEP". More of this chap in a moment.
The phrase is surprisingly recent in origin, despite the pre-war enunciation. It was apparently introduced as a pre-recorded announcement circa 1968, the terse phrase was also painted where appropriate on platform edges.
I was mildly surprised to learn that the clipped voicewe hear at Embankment is not standard throughout the system. Piccadilly line stations, for instance, use announcements pre-recorded by by Tim Bentinck, the actor best known for his role as David Archer in The Archers. His Wikipedia entry tells me that Timothy Charles Robert Noel Bentinck (to give him his full name) is 12th Earl of Portland, 8th Count Bentinck. He is also Viscount Woodstock, Baron Cirencester and "a mediatised Count of the Holy Roman Empire". Strewth.
At Paddington station we can hear the voice of one Keith Wilson, who was in 1990 industrial manager of PA Communications Ltd of Milton Keynes. It strikes me that we might consider having bespoke announcements recorded by different people at every one of our stations, perhaps based on local associations - Graeme Garden (Mornington Crescent), Suggs McPherson (Camden Town), Hugh Grant (Notting Hill), Sid James (anywhere else).
In March 2013 it was reported that the version recorded by Oswald Laurence would be restored to Embankment station so that his widow could hear his voice. This is the one I hear each day. You can find the full story here.
Incidentally the French version "Attention à la marche en descendant du train" ("Watch your step while getting off the train") is a perfect alexandrine.