They do not look like my bees at all.
If they're a cast from your hive, they'll look like your bees.If they are a swarm from one of my hives which I highly suspect now that I know they are not Cornish black bees then they have swarmed from a hive which has 4 supers on.
Or they might be a swarm from the beek down the road who keeps local mongrels. Not every colony in Cornwall is Cornish Black bees!