As I expect we all know, the grey squirrel (Sciurus carolinensis) is not a native British species, it originates from eastern North America (the scientific name of 'carolinensis' reflects this). It was introduced in to parks in Britain around the turn if the 19th Century. One of largest introductions was at Woburn in Bedfordshire. In the hundred years since then it has spread rapidly across most of the country with devastating effect on our native red squirrel. My reference book says it now 'infests' most of England and much of Wales and Scotland. 'Infests' is a strong word but probably does reflect the true position.
The problem with the grey squirrel is that it has a preference for the same habitat and food as the red to a point where the red's cannot compete. The grey has also brought a virus with itto which it hjas a degree of immunity but the red, of course, has not.
I have, on more than one occasion, had people say to me they have seen a red squirrel in their garden but of course this has not been the case. The grey squirrel has a chestnut brown face but that does not make it a red! They are very different in many respects and should not be confused by anyone who takes real notice.
The grey squirrel is now common in gardens that are close to woodlands (and some that are not) and although it is somewhat destructive and loves to tear bird feeders to bits you can't help be amused by its antics as it tries (usually successfully) to overcome any barriers put in way to keep from potential food supplies.
A villain, indeed, but surely an endearing one? After all, it is not their fault they are here - it is a man-made problem.