No Service, Return to Sender, 1941 addressed to Finland

The envelope below was posted from Bristol to Finland in April 1941 but received a purple "NO SERVICE / RETURN TO SENDER" cachet.  As there were no other cancels I assume that the cachet was applied in the Bristol Foreign Section (rather than in London)

The addressee was Lady Constance Malleson who subsequently wrote a book about her experiences administering relief efforts for the Russo-Finnish war.