On Apr 9, 12:44 pm, John B wrote:

* the trains must weigh less than 32 tonnes per coach

Yeah, like that's going to happen. I've just flicked through
TheRailwayCentre.com and it looks like only 315s, 508s and some ex-LUL
trains (all inner-sub units) currently meet that criterion. As for
outer-sub units, 317s and 321s would be approximately 10 tonnes too
heavy in 4-car formation (and the 319s up to another 5 on top) while
the 4-car SR Electrostars are almost 50 tonnes above the limit! And
don't even get me started on the Desiros and Javelins (well OK I don't
have the figures to hand but they are very heavy indeed).