Hi, the following is taken from the complete history of the british speedway.
Golden Helmet (First Division) raced for between 1965 and 7/5/1987 (Mitch Shirra given as last holder, Barry Briggs was initial nominated holder).
Silver Sash (First Division) raced for between 1964 and 1969 (Ivan Mauger has both initial nominated holder and last holder). The book adds that ths Sash was merged with the Golden Helmet in 1971.
Silver Helmet (Second Division) raced for between 1970 and at least 1990 (initial holder was Ross Gilbertson who defeated Ron Bagley, holder at end of 1990 was Andy Grahame).
I'm fairly certain that the Golden Helmet has been raced for since 1990 and that a Bronze Helmet was also raced for by Third Division/Conference/Amateur League riders since 1990 but can't remember when.