Barrel, bolt and receiver are from three different rifles, no doubt happened when the rifle was sported, although the rifle may have been rebarrelled while the rifle was still in service.
Churchill is one of the great names in British gunmaking.
Like a number of other firms, it fell on hard times following WW2. In 1958, the company name was acquired by Sam Cummings, surplus arms magnate extraordinaire. Cummings acquired the names of other old time British gunmaking houses at this time.
The sporterizing program dates from this period. Sam Cummings had LOTS of obsolete military rifles to market. The rifle is sported in much the same manner as the Parker Hale and other conversions. The Churchill name on the rifle is the only thing the rifle has in common with the classic shotguns that the original Churchill company made.
The current Churchill firm dates to 1994, and makes quality shotguns.