From TfL's live travel news page, details on LO line closures today...

---quote---
No service between Dalston Junction and New Cross Gate/New Cross on
Sunday 12 May due to Network Rail engineering work. [...]

No service between New Cross Gate and West Croydon on Sunday 12 May due
to engineering works. [...]

No service between Sydenham and Crystal Palace on Sunday 12 May due to
engineering works. [...]

No service between Surrey Quays and Clapham Junction on Sunday 12 May
due to Network Rail engineering works. [...]

No service between Highbury and Islington and Dalston Junction on Sunday
12 May due to engineering work. [...]

No service between Watford Junction and Euston on Sunday 12 May due to
engineering works. [...]
---/quote---


Thing is, the line twixt Dalston Junction and New Cross/ NXG is neither
owned nor maintained by Network Rail - it's owned by TfL London Rail,
and maintained under contract by Carillion.

Odd that Network Rail gets specifically mentioned up on a line it's not
responsible for, whilst it doesn't get a mention on the other lines it
*is* responsible for (ok, it does get a mention re Surrey Quays to
Clapham Jn, for which it is responsible for south of the new junction
located just north of Queens Road Peckham - which must have a name,
perhaps the Old Kent Rd Junction?).