• integrated headset and rear drop outs look 1940s/50s to me

    I'd say more 30's/40's The mudguard eyes and rear dropouts are a bit like a 1930's Claud Butler of mine.
    The "british made" bottom bracket shell is the same as the one on my father's late 40's Gillott - 1947 IIRC
    Splendid frame though very nicely filed/feathered lugs show the work of a decent builder - there's a surprising array of brazed on bosses for a 531 frame of that vintage.

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