Does anyone know if there any services that go from London to ashford and then turn Back? If so is there a way to identify these?
They go round in a loop. This was in the article at https://live.dovetailgames.com/live/train-sim-world/articles/article/tsw3-sehs-a-timetable-deep-dive and I think it covers what you're asking... I guess the bottom bit of the loop between Ashford and Faversham (full route map here) is missing, so you'd have to do it in two bits, or jump onto a service doing the loop in the other direction.
Most of the 1Js from Ashford form another 1J or 5J at St Pancras to Ashford (a few exceptions of course...) I just drove 1J13 and then the ECS back. However none do STP-AFK-STP