IEA Section 73

In order to ascertain whether a signature, writing, or seal is that of the person by whom it purports to have been written or made, any signature, writing, or seal admitted or proved to the satisfaction of the Court to have been written or made by that person may be compared with the one which is to be proved, although that signature, writing, or seal has not been produced or proved for any other purpose.
The Court may direct any person present in court to write any words or figures for the purpose of enabling the Court to compare the words or figures so written with any words or figures alleged to have been written by such person.
This section applies also, with any necessary modifications, to finger-impressions.

In order to ascertain whether a digital signature is that of the person by whom it purports to have been affixed, the Court may direct—

1. that person or the Controller or the Certifying Authority to produce the Digital Signature Certificate;
2. any other person to apply the public key listed in the Digital Signature Certificate and verify the digital signature purported to have been affixed by that person.