A tune composed by the late great flutist Josie McDermott. He played it on his "Darby’s Farewell" album. Peg McGrath was also a flutist.
According to the liner notes:
"He calls it an "instant" reel because it just came off the top of his head. One afternoon he had been playing a few tunes with Peg McGrath. Peg had been preparing a collection for a radio broadcast. That evening someone asked him to play ‘that reel of Peg’s’, meaning a standard tune she had been working on that afternoon. Before he played a note someone else asked if she had made it herself. He said she had, but he knew he could not play the well-known tune she had been playing. He put the whistle to his lips and this tune came out. An "instant" reel!"
Josie paired this with Ganley’s Reel, which I will hopefully post in the near future.
Here’s a nice version from the flute playing of James Carty.