The red squirrel is native to the UK, having been around since ice age and for thousands of years it did very well. Then in the late 19th Century wealthy landowners in England decided to introduce, as an ornamental species, the grey squirrel from America. However the greys have caused a massive decline in red squirrel numbers to the point where the reds are almost extinct from mainland England and confined to a few pockets in Scotland, Northern England and Wales. So why are the greys such a problem for the reds? Joshua Perry is Director of the Red Squirrel Survival Trust.