Later I managed to snap this chap at work.
A male Cardinal, very common in north America. We have no birds of such bright colouring in the UK; to me, he looks tropical. The Cardinal evidently fascinated earlier European settlers as much as it has captivated me, because this is the official bird of SEVEN States. I have also seen an American robin, red-breasted like his European cousin but clearly an altogether different bird. I wonder how homesick the early settlers must have been to name the American robin after an only slightly similar indigenous bird of Britain. Homesick, or drunk.
Naturally, I now feel quite smug about my decision to buy pricier squirrel-repellent bird food. This food is cajun flavoured - apparently the discerning squirrel has no tolerance of spicy foods. I have read that cajun food makes squirrels who do eat it more susceptible to hypothermia in cold weather. Well, whatever! That stuff is EXPENSIVE, so let that be a lesson to them!