In message , Mystery Flyer
writes

Was platform 1 at Clapham Junction ever used?

Yes, IIRC it was the original departure platform for services leaving
via the West London line (originally just to Kensington, but later there
were a number of others, such as the LSWR's roundabout route from
Clapham Junction to Richmond via Kensington and Hammersmith).

Trains would arrive at platform 2, detrain, and then pull into the
carriage sidings to the west of the station, where the engine could run
round the carriages and then pull back into platform 1 for departure.

--
Paul Terry