On this map https://maps.nls.uk/view/189259049 there is a single line siding leaving the main Brighton Line at about TQ 28724114 and curving away continuously to terminate by a rectangular building or compound at about TQ29104082 . It does not appear on earlier maps, although what this means is a bit obscure, as the revision dates for the map (published in 1961) are vague. There are no traces now, it is all under car park tarmac. What was it for?