It might be worth having a look through the Royal Mint Yearbooks for this period to see if there is any mention of it - https://library.royalmintmuseum.org.uk/archive/royal-mint-annual-reports
Thanks for posting that useful link.
I'm interested in getting information about the amount of 925 and 500 silver coinage that was withdrawn from circulation, and there seems to be some useful data - e.g. the following from the 1949 report: