Just a note for those wondering about getting to the depots early, trains serve selhurst 24/7, with all night trains from Victoria to Gatwick/three bridges making staff stops at Selhurst. so, if you are near Clapham, Purley, even horley you can get car park passes for most southern stations (not sure about clapham mind) and get there by train.
Note on car park passes, for most stations its one pass, for one car. though we at Brighton are allowed to have two cars registered into the system for the ANPR car park. You can also sometimes designate two stations to use. I live in Brighton, so dont, but many staff have passes for use say at both Lancing and Brighton, or Three Bridges and Brighton. So when you apply for your pass, pick your car carefully. Dont pick the car say the other half might want to use. Remember also that stations also have parking for motorbikes and scooters. A good way to get to work, and many mess rooms/signing on areas have places to change, or even to store your helmet. You will also get a locker to store stuff that will be big enough for leathers etc.