The most common squirrel within the UK is the North American Grey Squirrel (Scirus carolinensis) which was introduced to about 30 sites within England and Wales between 1876 and 1929 to control the Red Squirrel (Sciurus vulgaris). At the time the Grey Squirrel population was kept under control by the gamekeepers. Unfortunately, various wars meant that the gamekeepers were needed elsewhere and the Grey population grew out of control.
Today the Red Squirrel population has fallen to such low numbers that they are protected and are only really found in Scotland, Northumbria and the Isle of Wight