Pat Buchanan's "The Unnecessary War" argues that Britain had no reason to attack Germany in 1939. It could have allowed Germany and Russia to slug it out.

http://www.pacificaforum.org/lindbergh--fascism-and-world-war-ii

But this avoids the problem that Germany might have won. The British ruling class had a long term policy of preventing the emergence of one power on the continent. Two or more rival powers was OK - their rivalry would keep them in check, and prevent them from threatening Britain's interests. That's why Britain fought Philip II, Napoleon, the Kaiser, and Hitler.

http://www.telegraph.co.uk/history/world-war-one/10249760/Germany-intervenes-in-WW1-commemoration-debate.html

Of course, the masses of ordinary Brits had no reason at all to fight in any of these wars.