That saucer shaped object - and I'm guessing here, although I have worked in the defence industry for years so could be classed as an expert witness - is probably the London Eye.
A quick look at that seems to be a CH-47 Chinook flying right to left. Large rear engine cowl, small front engine cowl with a sausage shape in between. All IMO of course
On monday night me and my mate saw 2 fully loaded Apache helicopters flying over the common where we were running at the time. Fully loaded as well. Really an EPIC sight.