This is a British World War II British Intelligence Agency Cover.  It was sent from British Intelligence Agents in Lisbon, Portugal to Rufford, Lancaster, United Kingdom on 10/20/1943.

It was forwarded by Diplomatic Mail through the AIR MINISTRY.  It has a red P88 Censor.  This is a VERY RARE COVER!

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You have the option to have it shipped via regular or Priority Mail in the US, and Registered Mail overseas!  This does cost more, but it comes with tracking, and will help ensure the item reaches you in a safe and timely manner!