Bob Waterman adds "The headcode indicates 'via Dartford Loop Line' later described as 'via Sidcup'. From the date it appears to be a weekend electrification engineering works diversion - if a Sunday (which the date indicates) - of the 9.52 Victoria - Ramsgate which was the winter version of the' Kentish Belle' - hence the three pullmans in the middle of BR 4 set 'S' 870. If a Saturday this would be the 11.35 Victoria - Ramsgate"

These diversions could be routed via Bexleyheath, which of the three routes from London to Dartford is the next one to the north of this one - we do have a picture of N Class 31810 1959-05-30 on a Victoria - Ramsgate working via Bexleyheath (exact location unknown) on the previous day to this one due to the same engineering diversions. The headcode you will note is number 15 in that instance.