On a related subject, the current Southern tender for 130 emu vehicles is a short term stop gap measure (and probably a Bombardier gift as well), to fill the 2 yr gap until Thameslink stock is delivered. It will mean however that once that happens there will be 32 units needing to find some work somewhere, which could be on the Edinburgh Glasgow Improvement Programme routes, or alternatively may need some further route miles electrified to enable an emu cascade to occur. This could include the South Wales main line and Valleys.
It's also suggested by Tony Miles elsewhere that these will actually be ordered as 26 x 5 car units, which fits in better with Southern's 10 car inner suburban platform lengthening timescales - but
IMHO▸ it is just as likely that the net extra units (either these or the returning 377/5s currently loaned to Thameslink) could just displace something older from SN, such as 455s, 456s or 313s. It could kill two birds with one stone, because any of those other classes could provide carriages for
SWT▸ 's 10 car expansion - them being the major user of 455s.
Paul