I have little knowledge of Peter Kennedy, so cannot say anything from my own experience, but the following if correct shows how he had a profound effect on English music as well as song, and hasn't been touched on above. The following appeared on melodeon.net a couple of years ago (not written by me):-

Some years ago I asked Peter Kennedy to relate the story of the introduction of D/G melodeons into England as his name always seems to come up.

He said something like:

In the 1950s most melodeons were based in C with either F or G as a second row and the half row, often in the club format, to give more chromaticity. He was collecting songs and tunes in Northumberland and found strangely that much of the repertoire played by fiddlers in particular was of Irish origin and in G or D and sometimes A. He investigated and found that an anomolous reception of Radio Eirrean (sp) occurred in the NE and local players were picking up Irish tunes for their repertoire from the radio.

Now Irish melodeon players had adopted chromatic instruments based on C with either B or C# as a second row to enable them to play in other keys but this was not generally popular in England and the local melodeon players couldn't join in with this repertoire. So to help local melodeon players Peter arranged for Hohner to produce a batch melodeons in G/D, I believe that they were stocked and distributed by Bells of Surbiton and the EFDSS shop.

And it all followed on from there...