Section 69 of Evidence Act "Proof where no attesting witness found"
If no such attesting witness can be found, or if the document purports to have been executed in the United Kingdom, it must be proved that the attestation of one attesting witness at least is in his handwriting, and that the signature of the person executing the document is in the handwriting of that person.
Section 70 of Evidence Act "Admission of execution by party to attested document"
The admission of a party to an attested document of its execution by himself shall be sufficient proof of its execution as against him, though it be a document is in the handwriting of that person.