Dave Arquati wrote to uk.transport.london on Thu, 16 Dec 2004:

During the last Open House weekend, the DLR ran a train with a
commentary between Bank and Lewisham; it was very good!

That's not uncommon, I believe - I was on a train with one during my
ill-fated job in Docklands earlier this year. They ran from Tower
Gateway, and changed at Westferry. It was a tourist group, but they
used the on-train speaker system, so we learnt a lot even if we were
just commuters!
--
"Mrs Redboots"
http://www.amsmyth.demon.co.uk/
Website updated 12 December 2004