General Post Office Blue Ensign made of wool bunting with a linen hoist. It is hand-sewn with the details of the Queen's Crown painted. The letters 'GPO' are appliquéd in yellow in the fly. A rope is attached to hoist the flag.

In 1823 the Admiralty took over the management of overseas mail shipping from the Post Office and from 1837 it also managed the services within the British Isles. Contracts were allocated to new private companies and the old packet services went out of business. In 1837 the General Post Office employed a steam boat to collect mail from sailing vessels 'detained in the entrance to the English Channel, either by contrary winds or calms' and landing them in the first convenient port. The steam vessel was to be distinguished by a 'Post Office Blue Ensign'. Whether this was the blue version of the postboy ensign or this one is unclear (see also AAA0759).

The construction of this flag is consistent with a date around 1838 after Victoria came to the throne and the design of the crown changed. The size of the ensign indicates it would have been flown from a relatively small vessel.