I’m convinced I saw one of these this evening.
I was driving home and I’d stopped to make a phone call. The place where I stopped was right underneath the flightpath for incoming aircraft at East Midlands Airport.
You have to imagine the landing path running from left to right (basically, east to west). You usually see the planes banking in from either the north or south on the eastern (left) side of the flightpath as they take their turn out of the stack. At peak times there is about one plane every few minutes.
Well, at some time shortly after 8pm there was a plane travelling along the normal route from left to right (east to west) when another plane cut across from south to north. They were at the same altitude (judging by their relative sizes) and I can honestly say that they occupied less than an outstretched hand’s breadth of the sky. That is bloody close for a plane at such a low altitude, I’m sure.
Not seen anything in the news, though.