Why is it dearer to Buy British?

Ok, I know this is not a theologically inspiring question, but can anyone tell me why British bacon is more expensive to buy that Danish or Dutch?

I like to support British farmers, partly because I object to the pollution generated by the transit of food from one country to another. Our animal standards are some of the best in the world. I also know several farmers who struggle to make ends meet.  But I cannot understand why something British should be fifteen pence dearer than an import from 300 miles away.