What depots are accessable for photography,

I guess it depends on the level of detail you want in your photographs.

My immediate thoughts are:

Waterloo
Queens Park
Willesden (Overground)
Poplar (DLR)
Neasden
Ealing Common
Acton Depot
Lillie Bridge

Some of the above may require a ticket to access the locations I have in mind.

Croxley Wiggenhall Road Depot LOL - well at Acton in March!

Upminster depot can sort of be viewed through the fence from the car park, and parts of the buildings at Ealing Common and Golders Green are visible from the public end of the access road (a different view of the buildings can also be seen from the platforms at the latter).

There are several distant views of Beckton Depot from the road between Gallions Reach station and Gallions Reach shopping park. There is also a view from the entrance to the depot (on the same road), but the security don't like people hanging around or photographing.

There is a good view of Northfields from over the road outside Boston Manor station, and there is a good view of Morden from a public footbridge.

There is probably somewhere near Abbey Road DLR where you can see the outside roads at Stratford Market Depot, but I've not personally tried.

Hammersmith the best view is from the far end of the station platforms, similarly the end of the arrivals platform is the best public view of Waterloo depot.

Poplar depot, the best views are from the DLR and Ealing Common and Neasden also have good views from passing trains. The latter you can also see part of from station platforms and the entrance is visible from the footbridge alongside the North Circ.

There is a footbridge over the throat of Northumberland Park depot, but I don't know what (if anything) is visible from it.

Some great information there, thank you

Don't forget London Road.

The outside of the buildings are possibly the easiest to see from the street of all the depots. I don't know that there is anything visible of the trains from public areas though?

Also not mentioned yet:
Ruislip Depot - views of the outside roads from passing trains and maybe from the London end of West Ruislip station, I can't remember (the last time I was there it was foggy).

Hainault depot - views of some outside roads from Hainault station.

Cockfosters - maybe something with a long lens from Bramley Road (ouside Oakwood station), but I wouldn't guarantee it.

See [a href="[a href="herehere with strategically placed passerby for scale. You may need something to stand on. You can also get a good, though fleeting, view from the top decks of buses passing along St Georges Road.

Can`t believe no one has invented fold up rucksack ladders in this day and age