IIRC Astro training was binned for Gp2 Nav studes around the time that Finningley closed and the school moved to Cranwell.
Looking at my logbook, my last Dominie flight doing Astro was 30 October 1995 (a DM19 with 434 Cse).
Shortly after this, with the introduction of the new Dominie nav/radar fit, the Gp2 (ANTS) course was re-written to include an introduction to low level maritime work and most of the high level trog-exs also disappeared.