Well you can't argue that it would be an import if we did adopt it.
![Stick out tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Not that it is a reason in itself not to adopt it, but I just cannot see it working in our political system. Even the House of Commons chamber is seating plan acts against it! Would the unelected House of Lords be the guarantor of stability with the unstable House of Commons guided by self-interest? It would require a fundamental change which I'm not convinced the country is ready for. It would be better to reform the House of Lords, adopt PR in that chamber and see how it goes. If it goes well, then maybe adopt it in the House of Commons in twenty or thirty years time. What is the hurry? Rome wasn't built in a day, you can't expect us to wake up in tomorrow with a German style political system.
What evidence is there that it is done? It has always served Britain rather well, we shouldn't throw away centuries of tradition so lightly.