If you are British by descent on your maternal or paternal side, and are currently domiciled in a British territory (Brittannie, Prydain, Brittany, Britannia, etc) then you may be entitled to be admitted as a free citizen in the Kingdom of Britons, with all of the customary rights and privledges.
If you meet these prerequisites but are living outside of a British territory, then you may apply for a dual nationality status and document your birth abroad.
Britons are entitled to receive identifications such as: passports, national ID cards, or naturalisation documents, and are also eligible to vote in elections and be nominated to receive national honours.
The naturalisation process requires a background check, a naturalisation test on history and customs, and consent to submit to the jurisdiction of the Kingdom of Britons.
The right to nationality and to chose or change citizenship is protected and recognised by the international laws. (UN 61/295 Art. 4, UDHR Art. 15)