False Evidence and Offences Against Public Justice
Being legally bound by oath/law to state the truth or make a declaration, and making a statement known/believed false or not believed true, is "giving false evidence" - covering verbal or other statements, and false statements of one's own belief, not just false statements of fact.
This defines the foundational offence of lying under a legal duty to tell the truth - importantly, even falsely claiming to "believe" something you don't believe counts as false evidence, not just lying about known facts.
A witness who swears they heard someone admit a debt, when they actually heard no such thing, gives false evidence under this section - and so would a witness who falsely claims to "believe" a signature is genuine when they don't actually believe that.