I wouldn't be so sure, I think the UK is still capable of being a major player in international politics. The Britons have a relatively strong economy, especially since they didn't join the Eurozone. They also have colonies territories around the world, combined with their military bases and fleets around the globe. On top of that they have the Commonwealth of Nations and NATO. Alone their military is a force to be reckoned with, as Argentina learned the hard way, and they are one of the few countries that has nuclear capabilities.