The Red Squirrels Northern England project website has useful information on red squirrel ecology and conservation on its About Squirrels pages>>. They also publish several Downloadable Info Sheets>> including one about supporting reds in your garden and another on habitat management.
The UK Squirrel Accord has a Resources Library>>
For information including links to government reports, legislation and action plans, the website pages of the UK Red Squirrel Group>> probably gave the most comprehensive coverage, but more recently the information may not have been kept up-to-date.
There is also SquirrelWeb>> billed as the one-stop information centre for all your squirrel needs.