You need a current passport, your full birth certificate, the full birth certificates of the parent and grandparent your claim is based on, evidence that you plan to work in the UK, and evidence such as bank statements that you can support yourself. You may also need marriage certificates, deed polls or adoption papers.
The visa is open to Commonwealth citizens, British overseas citizens, British overseas territories citizens, British Nationals (Overseas) and citizens of Zimbabwe, aged 17 or over, who can show that a grandparent was born in the UK, the Channel Islands or the Isle of Man. A grandparent born in what is now Ireland before 31 March 1922 also counts, as does one born on a ship or aircraft registered in the UK or belonging to the UK government.
The documents do one job: prove each step from you to that grandparent. Your birth certificate names your parent. Your parent's names the grandparent. The grandparent's shows the place of birth. If any name changed along the way, usually through marriage, the paper that explains the change goes in too. Anything not in English or Welsh needs a certified translation; our birth certificate translation service covers the full versions that name the parents.