My fiancé always manages to surprise me!
I just received this wonderful addition to my
Christmas stamps collection.
The British Army had had a resident presence in Egypt since 1882. From 1932 to 1936 special seals were attached to the rear of letters to show that the letter was covered by special forces postal services. The two issues of interest to GB Overprint collectors are those issued in 1935 for King George V's Silver Jubilee and later in the same year for Christmas. It is arguable whether these stamps count as "GB Overprints". The argument in favour is that they are stamps issued by the British Government, supplied by them for use by British people, and are therefore "British stamps".
For a time these stamps were regarded as "cinderella" items, as they were treated by the Army not as postage stamps but as a receipt showing that the serviceman/woman had paid the special reduced rate postage and was permitted to post this letter, but only in the special forces postboxes. At this point the distinction from a "postage stamp" gets rather philosophical. They were stuck on the rear of the letter, not on the front, and inscribed "Letter stamp", "Postal seal", "Xmas seal", or "Letter seal", so as not to confuse Egyptian postal staff.