The book referring to the Falkland conflict, and the L42 being dumped in the stream is “Out of Nowhere - A history of the military sniper” by Martin Pegler on page 289 references 278. I agree with Peter and with Gil, not handing in a rifle you were issued with, broken or not is the worse kind of crime in the MOD armed forces.
As Peter correctly states the L42 had done two life times, 1945 – 1992 in the case of my the L42’s.