A purple flowered Geranium at Barnsdale Gardens in Rutland, UK. The plant is likely a hybrid or cultivar of Geranium psilostemon.
From Wikipedia (http://en.wikipedia.org/wiki/Geranium_psilostemon):
Geranium psilostemon, commonly called Armenian crane's-bill, is a herbaceous plant species in the Geraniaceae family. It is native from Turkey, Armenia, Azerbaijan, and the Russian Federation, and is cultivated as a garden subject, and a number of different cultivars exist. It has glowing reddish purple coloured flowers.