Applying for internal vacancies is now not a course of action open to trainees who joined after the course that the OP mentions.
Not that it would make much difference if it were open as internal vancancies ('VNs') are few and far between these days. Until fairly recently there used to be a permanent trawl for operational ATSA 2s at Swanwick plus vacancies popping up as ACPOs in the various sims all the time. They would give the chopped trainee a chance to get a foot in the door, get some experience and see what internal vacancies came up in the future. It's a sign of the times that there aren't looking for anybody now.
It's not a good time to be chopped trainee at any level.