Was passing through Richmond station yesterday at about 1400ish and noticed a 5 car cls378 in the LU platform (P7 I think) on the far side where the District Line trains normally park,
I was just wondering as to why this would be done
Not particularly unusual anymore; there is a restriction in place that means that the 'new' S7 stock LU trains cannot use P7 at Richmond. Although District line trains are currently formed of both D and S7 stock trains, the signaller has no way of knowing which are approaching Richmond, so
all District line trains are currently redirected into platforms 5 or 6, with platforms 3-4 used for London Overground trains and platform 7 generally used to stable LO services.
All generally speaking, of course. As ever, the signaller can (and does) alter services to use whichever platforms are required, albeit noting the S7 restriction mentioned above.