Manchus are ethnic Chinese. In fact they are completely Chinese.
There is no nation called "Manchuria", it is all within China. They speak Chinese, they follow Chinese customs, in fact you wouldn't even be able to tell the difference if you met one. There are only about 70 remaining native Manchu speakers in the entire world, the rest of them all speak Chinese as their first (and often only) language.
Manchus are Chinese. Ask them yourself.
Whereas British have not become Indians. It's the other way around, in fact, English is now the de facto national language of India.