Looking again at Keith's pictures, I can see a similarity to a basket hilt (such as you would find on a sabre or cutlass), but I'm pretty sure that these are just highly ornamental keys. Swords in heraldry are often very simple, with just a bar as a guard; that means of course that they can be shown point down, and looking like a cross. (Think knights on a crusade.....) The crossed keys are, of course, the keys to the gates of Heaven, and sometimes indicate that in earlier times a hostelry had a religious association. The use of the papal tiara would seem to indicate a continental rather than English origin. The empty cartouche would seem to indicate that it lacks or has lost an inscription. This is proving to be a real puzzle!