A crown was five shillings
Yes, but there was no crown coin in normal circulation, so a sum of 5 shillings was generally referred to as that, or as "two half crowns", not "one crown". Also two shillings was one florin, and often referred to as that. Prior to coins bearing the head of George VI, the two shilling value coin was marked "One Florin". It was also not uncommon for the sum of "one and six" to be referred to as "eighteen pence".
Crown coins were legal tender, but they were only issued to commemorate special events so were not in general circulation. Probably the most familiar one is the Churchill Crown, which is the only British coin ever to bear the head of anyone other than the reigning monarch.
To elucidate, or perhaps confuse, further, one shilling became five (new) pence.