I'd say it totally depends on which group you're listening to. Overall, I wouldn't say that there's a national tendency more towards one than the other.

When it comes to 'pure drop' playing - eg sessions in pubs - I doubt you'd hear much more harmonising at an English tunes session than at an Irish.

That said, something that muddies the waters here is that there's a hell of a lot more recordings of Irish traditional music than English.

So there's loads more recordings - both field recordings and studio recordings - of solo performers, duo performers and small group performers, across different decades and in different contexts.

Whereas with English music there's a disproportionate amount of 'contemporary' traditional music, relative to what came before. In Irish music, for every instance of The Chieftains or The Gloaming or Martin Hayes' groups you have a historic plethora of recordings of unison tune playing (with minimal harmony).

English music never really had that. With notable exceptions, English music - in terms of recordings anyway - sort of leaps straight from at-home recordings of Stephen Baldwin or Jinky Wells to the (not especially English) playing of Dave Swarbrick in various group formations; and the harmony-based arrangements of Wood & Cutting, English Acoustic Collective, Spiers & Boden, Tom Kitching and numerous others.

The contemporary fiddlers I just mentioned have their Irish equivalents - it's certainly not just an English thing to present tunes in harmony based group arrangements. But the big difference is that recorded Irish music is vast enough to have had many decades of different musicians so you get all the 'pure drop' stuff as well as the highly arranged stuff; plus all the nodal points along the way like piano accompaniment to Michael Coleman, bouzouki accompaniment (from Alec Finn) to Frankie Gavin etc