We never were a superpower really, even in the mid-19th century when it could credibly be claimed that Britain was the pre-eminent Great Power. Even before the First World War we were just one of a number of Great Powers, a label under which I’d (very unscientifically) also group France, Germany, America and Russia at that particular time. As others have mentioned above, we’ve been a second tier power since the 1950’s at least (and in many respects Britain was pretty weak internationally in the thirty years prior to that). Of course, fantastical notions about needing to maintain our ‘international role’, a legacy of our former status as a Great Power, played a key role in our decision to join the EEC in the first place and have formed a mainstay of europhile rhetoric ever since.
But vox pops during the referendum repeatedly made clear that a significant number voting for Brexit did so at least partly because they saw it as a way of restoring Britain's "greatness". And of course we did not lack for WW2 references (not least of the "PLUCKY BRITAIN STANDING ALONE" type) either.
