Actually that looks very like Dahlia Ruby ( a beautiful dahlia but can maybe lose form as the head expands) and is not a well known or distributed Dahlia, or maybe Dahlia Geoffrey Kent. For some reason I cannot post photographs, something I am doing I am sure, and I will try again.
I do not seek to disagree, but the Dahlia Arabian Night has a different form, colour, and has a velvety texture to the petals.
http://www.angliabulbs.com/dah...
This is a good photograph of the flower. I had it but it got killed by two years of cold weather and I have not yet replaced it in the dahlia line up. You have reminded me of it Greyghost, and I will seek it out again.