It used to be what they call a rusty rail move,not sure if its still timetabled to be done. I twas for checking the points from Hammersmith eastbound fast over to Barons Court and round to West Kensington for Picc emergencies or if a District line was routed down the fast, never heard of it going to High Street Kensington. All Picc line drivers are trained to do the move to West Kensington where we run empty as we have to overshoot the platform by about half a car then reverse back to Barons Court. The last time i did this was when we had the derailment on the Picc in Hammersmith sidings a few years back. Hope this helps
You can see for yourself, this is a video which came up as "recommended" and I immediately clicked on it when I saw the title. You can see it definitely runs High Street - Northfields depot and you can see in the OPO mirror at the start that it's definitely a bog standard 1973 stock - not the AIT or anything. Looking at the channel there's a video showing the run from Hammersmith fast to High Street, which matches up with your account of the rusty rail move.
I have a picture of one at Earls Court going towards High St Ken back from 2001. The driver accepted the wrong signal at Hammersmith and the points failed at West Kensington. It hasnt been timetabled to reverse at West Ken now for many years as the first District used to run from Ealing Common to West Ken and form the first Richmond.
I Spoke to the person who posted and recorded the clip. To clear things up they was recording a Picc line move from West Ken back to Barons Court on the west bound as part of the audio visual DVD that is for training new drivers to the line but there was a problem at West Ken so the train had to continue onto High Street Ken and reverse there.