zinao wrote:well he said he may have signed something. how do formal renuiciations take place? do you have to give back them your passport?do they cancel it?
To renounce one's British citizenship, one has make a formal application on the prescribed forms to the Home Office if in the UK or to a British mission (consulate, embassy and so forth) if outside the UK, and pay the required fee. Upon acceptance of the renunciation, a certificate is issued, in the form of the original application form being signed and stamped to state that the renunciation has taken place.
A successful applicant's British passport would be physically cancelled (I imagine), e.g. by cutting off the corner, but it would probably be returned to the applicant. (But old passports are often cancelled in this way when a new passport is issued anyway, so the possession of a cancelled passport doesn't prove anything.)
It is not possible to renounce British citizenship if that would render the person stateless. An application made on the basis of the expectation of gaining another citizenship is possible, but if that other citizenship has not been gained after six months, the application is deemed to have failed and British citizenship is retained.
The reason for my question was that many people (in the past, at least) have assumed that they have renounced British citizenship if they gain another citizenship or even if they apply for a passport of a different citizenship that they already possess (or even sometimes if they simply fail to renew their British passport when it expires if they are living abroad). Merely gaining another citizenship (e.g. by naturalisation) does not, however, mean that British citizenship has been renounced — as above, to renounce British citizenship one has to make a formal application to the British authorities to do so. Most British people who naturalise as the citizen of another country do not need to do this, and most do not do this.
Therefore (not even knowing the possible reason for any renunciation on your father's part), I was wondering why you would think that your father might have done this. Indeed, it is most likely that if he "is not sure" he did not do it, I would guess.