Table C { https://assets.publishing.service.gov.u ... ce_Gp2.pdf} of the suppoting documents section says that:
"Please provide the passport you entered the UK with or any foreign passport held and if the birth certificate you provide has not been issued by a British Embassy, High Commission or Consulate showing parents’ details, also provide evidence as shown in the below:"
If born before 1st jan 1983 then provide following docs:
- Both parents’ full birth certificates
- Your father’s naturalisation or registration certificate
- Parents’ marriage certificate.