We don't use crowns.A crown used to be 5 shillings, back before we were civilised.
(
Mu Dinofiddler,
Tue 7 Oct 2008, 0:41,
archived)
Also, according to wiki,the big five pound coins collecters fawn over are called crowns.
( Mu Dinofiddler,
Tue 7 Oct 2008, 0:48,
archived)