For those interested here's what I've found out via a friend who is actually writing a book detailing where aircraft on the UK register have gone.
Re the above , about XP688. XP688 was the last production T4. It served at RAFC Cranwell, 1962; College of Air Warfare, Mamby, 1964; moved to the Central Air Traffic School, Shawbury, by 1975. Moved on to 1 School of Technical Training, Halton, about 1990, as 9031M. Went to the a/c collection at Bruntingthorpe and thence to Botany Bay, Chorley, in early 1997. From there to the quary about 2000.
So, now we know.
Thanks everyone for the replies and interesting gen.