I recently came into possession of No. 4 magazine that is almost new (judging from overall condition and the lack of any visible wear on the follower). I thought perhaps someone here could shed some light on it's origins.

On the rear locking tab are the letter "A B" under the number "4".

The follower is marked "N.77".

There is a four digit serial number stamped on the bottom of the magazine, which I assume is unit level numbers as the numbers are struck almost casually in an uneven row across the bottom.

Can anyone ID the manufacturer for me? Or the country of origin if other than the UKicon? Many thanks in advance for any and all answers.
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