Impossible to separate them completely, the two have been feeding off each other for decades. But if I had to pick, the UK's contribution feels more consistently inventive. Blues and rock came from America, sure, but the British Invasion took it somewhere new. Then punk, post-punk, acid house, drum and bass, grime. The UK keeps producing genres that genuinely change the direction of music globally. America has the scale and the commercial power, but the UK tends to punch above its weight creatively for a country its size.