British crowns dated 1927-1937 were struck in 0.500 fine silver; the most common ones are the "rocking horse" crown of 1935 (silver jubilee of George V) and the George VI coronation commemorative crown of 1937. No crowns were struck between 1937 and 1951, or 1927 and 1902.
Prior to this, crowns issued in the 1800's and up to 1902 were sterling silver (0.925 fine).
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis