In message , Mark Brader
writes
The Northern line *had* skip-stop working before the war.
According to an LT booklet entitled 60years of the Northern published in
1967, Fig.23 shows a train on the passing loop at Brent. It says "This
service ran from 13 June 1927. The passing loops (at Brent) were taken
out of service on the 22 August 1936.
--
Clive