richardwpprn - On Sundays the STN-PMI originates in PMI, leaving there early am and returning at lunch. So I assume the aircraft goes somewhere on Saturday afternoon to fill the gap, perhaps one of the charter routes or MAN, and then returns to LCY early afternoon Sunday.
The Sunday STN-FLR does the same thing, again I assume the aircraft does or will do something from FLR on Saturday afternoons.
On Saturdays one of the STN-IBZ follows this pattern, originating in IBZ early morning and heading straight back there.