Seen similar over the fields near Mersea Island couple of years back. Just sat there, no sound, no blinking lights like you'd expect from a drone or helicopter. Stayed for maybe 4 minutes then just... gone. Not flew away, just gone.
What colour was it? That's always the first thing I want to know. The one I saw had this dull amber glow to it, not bright, almost like it was trying not to be noticed if that makes sense.
Post a sketch if you can, even a rough one on paper and photo it with your mobile. Details fade fast, trust me on that. Also worth checking if anyone else in your area reported anything, local Facebook groups are actually decent for that even if most of the comments will be idiots saying its a chinese lantern.