Where and (roughly) when?

It's 7 cars so I'd wager on it being on the Picc or Northern. Judging by the track layout however, it's 4 tracks, so must be on the Piccadilly.

Train number appears to be 234 or 334 - which according to my Picc WTT (although from 2001) would be a diagram to Cockfosters, which kind of matches with the illegible destination blind.

I'd guess time-wise late 60s to early 70s, prior to the introduction of 73ts.

Of course, I'm probably well out.

Mid-80s Bakerloo, on the Finchley Road to Wembley Park area?

EDIT: I'm stupid, it was the Jubilee on that stretch at this time, with 83ts.

I don't know, then.

Bakerloo just north of Harrow Weald, early 80s?

edit: arrgh, beat me to it ;D

When was the second siding removed?

Note the little lower-quadrant shunt signal as the outlet signal for the vacant siding (there was one of these for each siding). Just one of the delights of the old signalling system at Harrow & Wealdstone, and on the 'New Line' generally.