I sent this thread to Nick Sawyer, and got this reply:-
"If only Chadwicks knew the trouble they had caused! Below are some facts:
"Chadwicks ceased production of 477 in around 1965.
Frank did indeed have a substitute made by an American he met on the river bank. This same gentlemen still provides me with the substitute wool. It is the colour of the wool when wet which is important and this is affected by the colour and thickness of the copper wire beneath the wool. The colour of the wool is reasonably important but by far the most important element of the Killer Bug is the manner in which it is fished. I have tried many substitutes of suitable colour but the main problem has been the fibres rather than the colour - it is important to have the right thickness and the correct mix of natural to artificial fibres. I have no idea what the correct ratio should be, but high levels of artificial fibres make for a poor Killer Bug.
"Here is a handy guide for Killer Bug fishermen:
1. Get the technique right - it is possible to catch fish on a bare
hook if fished in a natural manner.
2. Get the weight of the Killer Bug right - it should sink quickly but
not so quickly that the current doesn't affect it.
3. The wool covering should be 2-3 layers only so that the copper wire
beneath the wool gives the Killer Bug a translucent appearance when wet.
4. It doesn't matter what colour the dry wool is, but when wet and
wound over copper wire it should be grey/brown with a slight pink tinge.
5. Did I mention to get the technique right!
Killer Bugs made with the substitute wool and a booklet on the correct Killer Bug technique are available from my website
http://www.sawyernymphs.comTight Lines,
Nick Sawyer"