But I found an interesting website by Guido Gonzato here: Guide to making low-tech whistles
Now I have found designs for whistles before, but I have had difficulty getting the same materials as were used in the original. If you substitute a different type of tubing it has an affect on the length and hole position. But I found 2 meter lengths of this 20mm diameter PVC pipe in B&Q and Wickes for 99p and 18mm diameter hardwood dowel which can be made to be a snug fit inside by sanding off about half a mm.
I made the Alto B-flat instrument, and I found that I needed to leave the tube about 1mm longer than was specified in the diagram.
In fact, because my tube started out quite long, I checked his overall lengths at F#, G, G#, and A and found they all needed to be 1mm longer than specified - that probably comes down to the type of tube, he says "not all PVC pipe is created equal".
Sorry I'm playing it a bit like a recorder, it's just to give an idea of what it sounds like! Guido has some much better sound samples on his website.
I'm intending to make some more of these, in different keys, and perhaps even longer and more mellow :-)
Anyway, if you like making simple musical instruments, I encourage you to have a go at making one of Guido's low-tech whistles.