Tom Anderson wrote:

How extraordinary. Surely it can't have been a very big sidings? Amazing
to think there was a little rooftop depot right next to where i used to
live!

Like many urban sidings, it was larger than you'd think. There isn't
much online about Holloway Carriage sidings, but I've found two images:

http://www.scienceandsociety.co.uk/r...image=10443326

and:

http://www.ingenious.org.uk/See/Transport/Railways/?target=SeeLarge&ObjectID={1D16F73A-AC28-28D3-B4ED-06543BAB1423}&viewby=images

There's also a reference in a railway accident report from 1951:

http://www.railwaysarchive.co.uk/doc...ingdon1951.pdf

This states that the 14-coach train was examined at Holloway Carriage
Sidings, which gives you some idea of the length of train that could be
accommodated.

There were about ten roads in there, IIRC. Holloway declined in
importance after Ferme Park and Hornsey became carriage sidings. It
was used for the Pullmans, and, along with Finsbury Park carriage
sidings, the non-corridor stock for the suburban services that were
replaced by the GN electrics. Finsbury Park carriage sidings closed
with the electrification, but Holloway remained open for at least a few
more years.