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This would appear to be the badge of the No. 300 Polish Bomber Squadron which
fought alongside the Royal Air Force and operated from airfields in the United Kingdom.
Above: Badge with colour. Source: Wikipedia. Below, badge (no colouring) on memorial plaque. Source: Aircrew Remembered
The CCC is 300 in Roman numerals and the badge
combines the coats of arms of both Poland and England - it has the Polish White Eagle "OrzeΕ BiaΕy" (an eagle argent armed, crowned) and it has the English Lion (a lion passant guardant, crowned).
The squadron was created in July 1940 and disbanded in February 1947. They flew Fairey Battle light bombers until November 1940, then Wellington bombers until March 1944 and finally Avro Lancaster bombers.
There is a website dedicated to the squadron here with a lot more information than the Wikipedia pages. Among the many targets they bombed was Berchtesgaden, Hitler's retreat.