How long have Grey Squirrels lived in the British Isles?

We only have red squirrels here on the Isle of Wight

And now we’ve got black squirrels but I don’t know where they come from.

The Duke of Bedford has a lot to answer for starting with my chewed up bird feeders. Thanks Duke.

grey squirrels are carriers of squirrel pox, but they're immune to it. Red squirrels are not.