On the stamp/chop that they put on your passport, did it state "Leave to enter for six months" or words to that effect?
Something like this?
If you do not have a BRP or an ILR vignette in your passport, you are not free of immigration restrictions and hence can not apply for British naturalisation.
Are you of Chinese ethnicity (because China considers people of Chinese ethnicity to be automatically Chinese citizens) or have you ever held any other nationality (by being born in a country with
jus soli, such as most countries in the New World, for example)?
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.