In article , Trolleybus
writes
Neasden was a Bakerloo Line depot but the Drayton Park - Moorgate line
was advertised as being part of the Northern Line. Was it
operationally part of the Bakerloo (in the way that the ELL was
advertised as Met Line but was operated by, was it the District)? Or
was it worked as Northern Line but went for overhaul via Neasden to
Northern Line depots and Acton?

It was operationally part of the Northern Line at this point, but
getting stuff to Neasden for heavy overhaul was much easier than getting
it to any Northern Line depot (from Farringdon you'd have to go via the
Circle to Earl's Court, then Hammersmith (reverse), Piccadilly to
somewhere at the east end (reverse), back to King's Cross, then King's
Cross Loop to Euston (City), then to wherever.

--
Clive D.W. Feather