Today was my 3rd visit to the British Wildlife Centre in Surrey. There really is no better place to get photographs of red squirrels.
If you do go, I strongly suggest however, you arrive early because the squirrel's are fed at 10:30 and after they've had their fill and done their showstopping theatrics, I'm convinced they go back to their hides, put their feet up and watch a bit of TV, and then you barely see them for the rest of the day, so get there early!