Daily commissioning runs to Luton or Bedford during daytime and overnight test runs in the early hours, 4 sets stabled at Cricklewood all viewable from passing trains between Cricklewood & Hendon stations (12 car and 8 car nearest mainline, 8 car behind that, 12 car furthest from mainline) Blackfriars at Lunchtime also a good place.
One of the better locations to film arrivals and departures from a comfortable and legal position is the toip floor of the St Albans station car park. You have an unrestricted view of the northern end of both slow and fast platforms.
- the platforms have been extended for 12-cars now which means that the front of the train is better viewed north of the staircase tower, (see departure from the station). Looking at Youtube, it seem that many others know about this photo viewpoint too.