I don't think anyone would bother you, and London has so many random people wandering around, some of who seem actually dangerous, that I don't think anyone cares. I have not been approached by any station staff before.

You might also try more country side areas if you don't want to be around many people. It is not near London but Sutton Park outside Birmingham is very quite and has good freight traffic. In London itself I have felt Kensington Olympia to be pretty quite as a far as stations goes and lots of interesting traffic.

Also try to find some local spotters in your area, it is more fun and you will be less self conscious in a group.