Robert Waterman says "There is no evidence of the forthcoming electrification which took place in June 1959 and the signals are lower quadrant - they were upper quadrant by then.
This is the Thanet/Kentish Belle which ceased running September 1958. This is the Thanet Belle which only ran between 31 May 1948 and 24 September 1950. From 2 July 1951 it ran as The Kentish Belle.