"Spelled" is more common now even in British English. E.g. compare a Google search of 'site:bbc.co.uk "spelt"' with 'site:bbc.co.uk "spelled"'. Most recent usage of "spelt" is referring to the grain, or a direct quote of somebody who prefers the old-fashioned spelling.

Dr. Johnson gives both spellings in his Dictionary, along with relevant quotes from Milton and Dryden, which are all spelled "spelled" or "spell'd".