Hello Alan,
Cogswell & Harrison .242 Vickers likely made for/by Vickers-Armstrong and retailed by Cogswell & Harrison, Ltd. on or after 1932.
Serial number 4017 (a Vickers serial number because Cogswell & Harrison says that they used 5 digit numbers?)

find details here in "Rifle" Forum:
http://forums.nitroexpress.com/showflat.php?Cat=0&Number=330933&an=0&page=0#Post330933