Married in the UK
If you got married in the UK, you should be able to provide your marriage certificate. If you cannot find your marriage certificate, you should obtain a replacement from the relevant local Register Office.
Married outside the UK
If you got married outside the UK and cannot reasonably obtain your marriage certificate or were never issued with one for whatever reason, you should instead provide a sworn affidavit or other legal document that can demonstrate your marital status.
A sworn affidavit is a written statement made by a person who is under oath to tell the truth about facts and information contained in the statement. Additionally, the person signing the affidavit, called the affiant, attest to his or her identity.
Usually, the affidavit must be witnessed and signed by a person who is legally authorised to administer oaths, such as a notary public or another qualified official, such as a court clerk, solicitor or barrister.
A notary public, sometimes called a notary or public notary, is an individual authorised by the state or local government to officially witness signatures on legal documents, collect sworn statements and administer oaths.
Failure to provide any of the relevant evidence will result in the assessment of your application being delayed.