The above is an image of a Standard presently kept in storage at the National Maritime Museum. It is the only known survivor from the Navy of Cromwell's time (The State's Navy, not the Royal Navy) and is thought to be the Standard used by Generals at Sea (senior admirals), the most well known of whom were Blake, Monck and Mountagu. The escutcheons which have within them the St. Georges Cross and the Irish Harp seem to be upside down: the harp 'looks' to the right rather than the left as in nearly all other flags; and the wreath is asymmetrical (thought to be palm for Victory on the left and laurel for Peace on the right).
One theory is that it was run up as a prototype and rejected because of the abnormalities, put in a chest and forgotten, thus surviving the wholesale destruction of Commonwealth and Protectorate images at the Restoration of the Monarchy in 1660. Opinions on whether it was ever flown (based on fibre analysis) are varied.
I have been collecting information and theories about this standard and I would welcome any from this forum. I was lucky enough to be allowed to see it last year, and I have some close up photos which anyone is welcome to see if they PM me.