Dave Newt wrote:
What was the train I got on today on the District Line?

Outside, it was in the white and blue colours. It was kind of
Victoria Line shape and size (not the bigger-looking D(?)-stock.)

Inside, it had green grab rails which I have never seen before (more
than usual too), it had Central Line-type door buttons, and it had
orange dot-matrix displays like the Picc ones, but these were in the
middle of the cars hanging transverally above the corridor.

It certainly wasn't brand-new, but I've never seen it before.

What was it?

It sounds like the prototype refurbished District Line D-stock car
17008. AFAIK that's the only one with green grab rails, and it also has
a dot-matrix display and new door buttons. The adjacent cars 7008 and
8008 have been painted externally in standard LU livery as well, but
only 17008 has been refurbished internally. I think the repainting may
have caused you to think it wasn't D-stock.

It remains to be seen whether the general refurbishment of D-stock will
look the same. The first 6 cars are being worked on now, and are
planned to enter service this summer, according to Metronet.
--
Richard J.
(to e-mail me, swap uk and yon in address)