This is a Tangier Registered OHMS, or On His Majesty's Service Cover.  This one was sent on 6/15/1935.

What makes this little guy really special is the usage of the Tangier Silver Jubilee Issues.  These are SG 238, 239, & 240.  They are valued at L33 x 6 = L198!  In addition, there is a CDS and receivers on the back. 

THIS IS A STUNNING COVER!