Hi John,
The place was in trouble around the time that NEI collapsed, and the business passed to Rolls-Royce in the late 1980s, and then to Siemens a few years later.
It didn't help either Parsons or their arch-rivals GEC that one of their mainstay customers, the CEGB, was itself being dismantled in the early 1990s and few if any domestic orders for large steam turbines were placed during that period. I watched one of the last big sets leave the works in 1985(ish), probably heading to Drax in Yorkshire although I didn't know it at the time.