What is the test to be applied by an appellate court to an assessment of the decision of the trial court in respect of a statutory defence of “lawful excuse” when Convention rights are engaged in a criminal matter?

Analysing Director of Public Prosecutions v Ziegler and others [2021] UKSC 23 case from the perspective of Natural Law Jurisprudence

What is the test to be applied by an appellate court to an assessment of the decision of the trial court in respect of a statutory defence of “lawful excuse” when Convention rights are engaged in a criminal matter?

Is deliberate physically obstructive conduct by protesters capable of
constituting a lawful excuse for the purposes of section 137 of the 1980 Act ,
where the impact of the deliberate obstruction on other highway users is more than de minimis , and prevents them, or is capable of preventing them, from passing along the highway?