My back garden seems to be host to some kind of rodent, which is living
on seed that I put out for the birds. I dont see it for very long so
cannot describe it in detail, because it darts out from behind the shed
eats a seed or two and then retreats just as quickly.

My initial instinct is that it is a rat, but it does not have what I
would call a rats 'face' which is pointed and similar to a mouse (only
much larger). It has more of a rounded head, like a grey squirrel. In
fact its head and body are very squirrel -like and of a similar size,
but it has a long rats tail.

Should I be concerned? Do I need to call the council exterminator, or
maybe hire the neighbours Jack Russell? Or is it just some harmless
species that I have not come across before?