Southeastern. Badly.
Some of, if not the biggest housing and population growth in the UK. No new metro stock since 2006. Crossrail alleviates one line which is seeing mass housing development further along anyway (Charlton, Deptford, Greenwich etc). Current services restricted mostly to 10 car as running 5-car 376s or Networkers without SDO, despite millions spent the past 3 years on making the Network 90% capable of 12-car running.
319s are a nice short term fix but that frees up more networkers, which don't have SDO so unless something happens there not a great solution.