Why is white the opposite of multicultural? French, German, Italian, Polish, not to mention British, they're all white, but also of different cultures. Many rural areas attract people from predominantly one area over others so you get pockets of one ancestry over another.
Also, one need not live near other cultures to have exposure to and experience with other cultures. One can travel, or have lived in another part of the world and have been immersed fully in other cultures but now reside in such places as you describe.
Lastly, such areas as you describe pretty overwhelmingly vote Conservative, don't they, so why do you care?