dragartist,
according to my logbook the last HSP I dropped was on September 26 1984 ! XV 186 was the a/c operated by JATE. I have a pic somewhere I think. This was after Op Corporate so someone must have decided that the capability was still needed in the light of lessons 'learned'.
I have a vague memory that the only reason one platform survived was that it was 'hidden' away in a corner of the JATE hangar and not scrapped.
I can not recall any being dropped after this date but stand to be corrected.