No one had a go at identifying this plant. Admittedly the photo does not clearly show the leaves which may have helped.
This is a hardy hibiscus which does very well in cool temperate climates. It is deciduous loosing all its leaves in winter. It is particularly attractive when in full flower when it covers itself in hundreds of flowers about 75mm across. There are about 300 cultivars in the world. Colours range from pure white to dark purple. Flower shaper is from single open flowers to large multi double flowers as shown.
This is a great versatile plant that would grace any garden.