I didn't manage to make it home this week to have a look, but re the Chinese lanterns, yup there is a "bad person" 'round Saaff London who lets
off dustbin sized ones. Scared the bejesus out of me the first time I saw one, so be careful. The thing(s) the OP and I saw were high up (and in my
case) diffuse.
Just want to say to any "fun" types out there, launching any type of "lantern" into the take off volume from City or the approach volume to LHR is
not a good idea. One low altitude dustbin bag into an engine on take off or approach is going to be messy.
OK saw one last night moving approx north east at approx 19:00.
Big, bright, orange and quite fast. It's altitude was below that of the LHR planes coming off the stack but would have been pretty close to the
height of anything taking off from City.
I believe what I witnessed that night was a chinese lantern as I purchased a couple back in March and released them and they looked exactly the same
as this light that I see.