This has probably been told before but is worth repeating.
All these Low D whistles are derivatives of the hallowed Overton. Before Overton there were only the Generations and Clarkes penny whistles. Bernard Overton invented his Low D (and later complete range of whistles) sometime in the 70s at the request of Finbar Furey. The Fureys were living in Coventry at the time, and Bernard was well-known on the local folk and jazz scene. He was also well-known for doing a bit of welding, and regularly fixed folky cars that had failed their MOTs. Finbar Furey used to play The Lonesome Boatman on an old bamboo whistle, which was not in concert pitch. He apparently sat on it at a party, and went to Bernard to see if it would be possible to construct one out of metal tube, that would sound as sweet as his bamboo one, but be louder and even better be in tune! And also be indestructible.
A tall order, but Bernard set to work experimenting with steel, aluminium, copper and finally stainless steel tube, and the result was something like the whistles you see today. Initially, he only built the whistle for Finbar, but as a result of Finbar playing it all around the World, people kept phoning to ask if he could build one for them. Bernard was not a whistle player (although he does play now), but played piano in a jazz band and nylon strung guitar at the local folk clubs.
Through a happy accident, his experiment grew into the industry that it is today. And despite all the other derivatives there are around, he is still as busy as ever and struggles to keep up with demand. Now in his mid 70s and suffering from arthritis, Bernard is still working in the workshop alongside Jim Webb, who does most of the day to day work. There is no inbuilt obsolescence here either - these whistles are indestructible.
So where have all these whistlers come from?
If you want to know more, go to Phil Brown's excellent Big Whistle Music website.