Known as red horse-chestnut here in Southern England. Used to be many where I lived as a child, but not so many now. Quite a spectacular tree when in flower amongst all the greens. Great photo BTW.
Michael F will correct me if I am wrong but in UK the American Aesculus pavia....buckeyes are very rare. The red flowered tree here is Aesculus x carnea briotii. aesculus x carnea briotii - Google Search
Totally agree Silver surfer, I last remember seeing one in the late 50's at a place called Southampton Common. It did stand out, hence why I remember it.
Yep - Tlairmore's pic is Red Buckeye Aesculus pavia; the tree called Red Horse-chestnut (Aesculus × carnea) in UK is a hybrid between this and [Common] Horse-chestnut A. hippocastanum.