There are a couple of highlights that I do want to mention. First, conservationists who demonize the grey squirrel for causing the decline of red squirrels in England tend to ignore the role of habitat alteration and loss in their decline. Grey and red squirrels typically inhabit somewhat different environments: greys favor deciduous forests, while red squirrels prefer conifer forests. Over a period of centuries, due to both climate change and agricultural and urban development, conifer forests have largely disappeared from all but the northern reaches of England and Scotland. The remaining deciduous and mixed forests and park lands are more favorable to the grey squirrels. Thus it is not surprising that the remaining strongholds of the red squirrel are in the north, primarily in Scotland.
Second, Professor Acorn's site makes a compelling argument against the assumption that the grey squirrel is responsible for the spread of squirrel pox virus, and points to evidence that the disease was present in the early part of the twentieth century among red squirrels in areas where they had no contact with greys. He also argues that grey squirrels have developed immunity to the virus over time. Red squirrels could do the same, he argues, but have been unable to do so because in England they are weakened due to living in a marginal environment for them, one that has been made even more marginal due to alteration by humans.
Again, this is a fascinating site that counters many of the arguments of the "conservationists" in the UK who advocate the killing of grey squirrels. Please give it a look.