Bob Adams wrote:

You appear to have overlooked the 313's, which are not exactly in
their first flush of youth.

A very good point indeed. I must have been having a senior moment! ;-)

The 313s aren't the finest piece of equipment in the world by a country
mile. Typical 1970s BR austerity kit. Of course, the 313s, 314s and 315s are
now the oldest a.c. equipment on the network, in fleet service. There is
talk of TPTB north of the border funding replacements for the 314s in the
next 4-5 years. No doubt the 313s and 315s will be coming up for renewal not
long afterwards, they will be over 35 years old by then. I suspect that the
Silverlink 313s may well not find another home once that operator (or TfL,
in point of fact) has no further use for them, once the Electrostars have
taken over.

Perhaps that would be the solution - an add-on order of high-density
dual-voltage Electrostars to replace the 313s and a fleet of the
lower-density mainline ones to replace the current long-distance/outer
suburban stock. It would certainly be a political solution, keeping Derby in
production around the LUL fleet replacement programme - although our friends
in Germany and Japan might have other ideas.