Putting to one side for a moment the sheer improbability of Operation Sealion actually working (which I strongly suspect has been pulled to pieces on this forum before) I've always wondered which British composers, precisely, would receive the imprimatur of whatever German administration could be scraped together in the event that they managed to annex Great Britain.
Percy Grainger's an obvious choice given his interest in Nordicism (although I think he was still in Missouri as of the outbreak of World War II). Constant Lambert and William Walton were both active during the Second World War, and it's entirely conceivable that they could be strongarmed into producing music celebrating the new regime: Delius had died recently enough to be musically resurrected as the official composer of a Nordic Britain (especially considering his interest in German and Norwegian composers) but I strongly suspect he'd be pigeonholed, rather like Richard Strauss, as a hopeless and morbid decadent entirely unsuited for the new and glorious era of National Socialist Man. Can anyone else think of a possible official composer for a National Socialist Great Britain?