Right so this is exactly the kind of thing I've been saying happens way more often than people report, most folks just don't bother posting because they're worried about looking daft.
Few questions before the usual crowd starts shouting swamp gas - how long was it hovering roughly, and did it make any sound at all? That second bit is usually what separates the interesting ones from the boring ones in my experience.
Had something similar over Heaton Park about three years back, completely silent and just sat there for maybe two minutes before it was gone. No strobing, no navigation lights, nothing conventional about it. Still haven't got a decent explanation for that one.
Definitely worth getting a decent camera set up in your garden for the next few nights, these things do tend to revisit the same area. Anyone else in teh Manchester region seen anything lately actually?