Platform 4 at High Street Kensington station

It has a very narrow staircase!

I don't remember the wood and glass screen being there, well not in the early 1970s. There used to be a bit of over-run towards the dead end but that I believe was for the Jinty to run round with the col train to the goods yard. (what goods yard I hear you ask)... where the hotel is there was a huge goods and coal yard, you can still see the approach to the right side at the end of platform 4. There's a separate thread about it on here somewhere.

To hijack this slightly: anyone know the last time this platform saw a C-stock?

The last C stock to use High St Ken Platform 4 should have been on Monday June 2nd, the last full day of C service: train 72 arr 0518 ex Wimbledon, departing at 0529.  I video'd the working here a few weeks previously.  
Regarding the extension of the track beyond No 4 platform end, which still survives, this was to allow for the sometimes quite long Midland freights to clear the point for the reversal into the goods yard.  In that confined space a Jinty opening up for that brief but steeply graded propelling manoeuvre must have been quite something to behold.  Recently published by Ian Allan, 'Twenty Five Years Of London Transport 1949-74' has a useful but undated photo on p14 (lower) showing the trace of the already lifted siding but with the arch roofed goods shed still in place before the site was developed for an hotel, etc.  Unfortunately the author's caption only refers to the Q stock District train in the photo and makes no reference whatsover to the interest value of the location, which apart from the goods yard shows the train emerging from the District tunnel and crossing over to the Met/Circle tracks.