@hightor,
These squirrels are descendents of breeding pairs released in Bournemouth in the 1920s.
They are classed as invasive and have pushed the native reds out of a lot of areas including Southampton.
Now areas with red squirrels are conservation areas.
I think our greys are descended from American squirrels but I'm not 100% sure.
Those are the ones I'm feeding and if they look familiar they probably are American greys.