English Traditional Music
English Traditional Music is not as well defined as almost anyone elses. Irish, Scottish, Welsh, Breton, Nova Scotian, etc are quite distinct and relatively easy to define. It is definitely a minority sport compared with the massive popularity of Irish Traditional Music.
The closest that I can get to it is that is a mixture of influences played on certain instruments for (usually) certain dances which have become characteristically English and typically underplayed. Like the English language has absorbed words from many cultures, English Traditional Music has taken on many, many styles, rhythms, tempos and nuances so that it is what it is. It isn't (and probably never was) a pure tradition. Whatever came along, ordinary people absorbed into music and dance for both social and display dances.
Many of the Country Dances are derived from the French or at least Continental European court dances and are no more than 200 years old or thereabouts. The Waltzes, Polkas, Gallops, Schottisches, Redowas, Mazurkas and many more fall into this category. Reels are a little more problematic and certainly Scottish and Irish influence is felt. Possibly the Jig is the earliest and most original form of dance and music, but even this has possible French connections.
I would refer you again to John Kirkpatrick's wonderful article: What is English Folk Music?