I found this on the web:
http://www.overthegardengate.net/wildlife/squirrel.aspThe red squirrel (Sciurus Vulgaris)
The only squirrel native to Britain, it can easily be recognised by its size, colouring, and especially in winter, its large ear tufts. The colouring can vary from bright ginger, red through dark brown, and can be tinged with grey. From nose to tail, their length is around 350 - 400mm, adults can weigh up to 350g.
The American grey squirrel (Sciurus Carolinensis)
First introduced to Britain at Henbury park, Cheshire, in 1876, and introduced to other areas around the UK in the 1920s.
From these sites the squirrel population grew, and as it did, the red squirrel population began its decline.
There are no definite facts as to why the two species cannot live together, but it appears that the greys have a greater ability to compete for food. The only advantage that the reds have is their supremacy in conifer forests.
The British red squirrel population is estimated at 161 000 - 10 000 in Wales, 30 000 in England, and 121 000 in Scotland.
The grey squirrel population is estimated at 2 520 000, with two million in England.
In England, greys outnumber reds by 66:1.