Certificat de nationalité

Hi, I need to get a Certificat de Nationalité (from the British Consulate)

Problem is, the consulate do not know what one of these certificates are, at least that is what the operator told me. Looking at the consulate web site does not help, as the closest I can find is an Actuaral Service for 'certificates of existence'

Can anyone tell me if this certificate is known by some other name ?

Thanks