The thing about Britain is that it could always change when change was necessary. It did not resist change and experience revolution as a consequence. When it came to tolerance, Britain was ahead of the rest of Europe. Hence in the late nineteenth century, European radicals such as Karl Marx, Kropotkin and other sought refuge in Britain. As for the slogan "American imperialism" - just a cliche from the left wherever you go.
I agree. Evolution, not revolution in government is the most remarkable example set by British democracy. But there are many others. Britain needs to get over losing colonies and get proud of itself again.