The concertina has a claim, being the only instrument invented by an Englishman.

The instrument most commonly associated with English folk music and less with any other type of music was the Hohner pokerwork D/G melodeon for many years.

I reckon GS is on the money with his brass bands too.

Let's not forget that England has a church-based choral singing tradition that is the envy of other countries, and a bell-ringing tradition that is uniquely English, not only church bells but method ringing on handbells.

Anahata