Thanks to everyone who has suggested starlings or swifts. Here is
"I thought of starlings. The aerial display wasn't all in one bunch.
There were 3 spires of living things going up and down with a cluster
of dots at the bottom connecting the spires. It could be described as
3 chimneys of black dots with the chimney on the right being the most
populated. Anyway it was unusual and I was just hoping someone else
may have seen them. Perhaps starlings, perhaps swifts, perhaps a swarm
of locusts readying for the financial disaster about to hit."
Am I right in thinking this sounds more like swifts?