Saw this as I took a rare trip up to cockfosters today, never noticed it
before - must have been behind vegetation. There's very little about in
online other than it was meant to defend the depot. I'm no military expert
but I can't really see what its purpose would have been. If the germans
had got to cockfosters then it would have been game over for the tube and
probably the country so what was the point?

Anyway here's a google maps link:

https://goo.gl/maps/i4A26d931KctSoVy7