I found a contemporary British source for you: Considerations on India affairs - William Bolts - Google Books, published in 1772. The passage mentioning thumb-cutting is at the bottom of page 194. However, it was "winders of raw silk" not weavers, and it wasn't to end weaving in India, but to enforce the British East India Company's monopoly (all weavers were to work for them through exclusive deals).

_{*Lunatic*, n.
One whose delusions are out of fashion.}