False Evidence and Offences Against Public Justice
(1) Threatening injury to a person (or someone they care about) to induce them to give false evidence is punished with up to 7 years' imprisonment, fine, or both. (2) If an innocent person is actually convicted and sentenced to death or 7+ years as a result, the threatener faces the same punishment/sentence as that innocent person received.
This criminalises coercing a witness into perjury, with the threatener's own liability escalating to match whatever severe consequence their coercion actually caused an innocent victim to suffer.
Someone who threatens a witness to force them into giving false testimony that results in an innocent person's wrongful conviction faces the same severe punishment that the wrongly-convicted victim received.