But not everyone had been convinced the eye-catching image looked like a British scene.
It has now emerged that the main photograph used seems to have been taken by a German photographer.
Some elements of the poster appear to have been taken from the below still, available from a photographic library.
It was taken by a German photographer, Alexander Burzik, in 2008.
Channel 4 News contacted Mr Burzik today, and he said the original photograph was taken in Germany not far from his home town of Weimar. He said that the version in the poster had been digitally altered.
Tonight a Conservative source said that the poster was based on a variety of images, and they had been previously assured that all elements of the photograph were British.