On 25 May, 11:50, "Dr. Sunil" wrote:
Hopefully self-explanatory!

http://commons.wikimedia.org/wiki/Fi...Haggerston.jpg

I take it these are original 378/0s (dual voltage) with a fourth car?

This is the first of the extra 4 car dual voltage units ordered after
the initial 24 x 3 car dual voltage (001-024) and 20 x 4 car DC only
units (135-154). These extra units (225-234 and 255-257) have been
ordered in bits and pieces as the various extensions to the ELL have
been authorised (some for the Highbury & Islington bit, some for the
Clapham Junction bit and some for service strengthening on the North
London Line).

The 3 car dual voltage units will be extended to 4 car at some point
(once the infrastructure works have finished) and be renumbered
201-224.