I did three years as the Flight Aircrewie. Great times. FI's patrol, DTS - only bad thing was it also covered the Wasp disbanding in 88.
Agree it wasn't the Leander F15. (I think). Maybe this one! https://en.wikipedia.org/wiki/HMS_Euryalus_(42)
But I suspect one of the sages of yesteryear will have some info.
"What's it made of, please, and what is the diameter? I think it's not from the (Leander class frigate) Euryalus VI as I would have remembered it from my two years in her." Made from aluminium
40cm in diameter