I'm experiencing garden envy and inspiration at the same time. What a magical place. I've visited the UK a few times. I'm always amazed at the beauty. Butterfly bushes even survive by train tracks. My favorite magazines: http://www.gardensillustrated.com/
Click on the photo for a better view. Check out the tall purple plants.
They are verbena bonariensis. I've had reasonable success with them here. Its best to offer them some wind protection. They add a nice architectural effect to your garden.