Well it wouldn't have to be the most played. I'm sure lots less people in Scotland play Bagpipes than Electric Guitar but most Scots know what the pipes are.

Today in 21st Century England there could be many instruments that fit the bill. Obviously fiddle - played a lot now but also played in England for hundreds of years and recognisable to most - would be a good candidate, as would the guitar, G/D Melodeon (recognisable to many), and whistle (though many might think it Irish). What relevance obsolete Elizabethan instruments have to 21st century England I don't know, and for those into tradition - I'm sure my great-great grandparents wouldn't have thought them relevant to the 19th Century either.