Under the Criminal Damage Act 1971, no offense is committed if there is a "lawful excuse" for the damage.
The defence argued that there was a lawful excuse on several grounds:
1. The defendants believed they were preventing a more serious crime (public indecency because of the statue's offensiveness).
2. The defendants believed the statue was owned by the citizens of Bristol (as stated on its plaque), who they believe consented to its removal.
3. Their right to freedom of expression and assembly under the European Convention on Human Rights.
The judge instructed the jury that they were allowed to consider questions such as the statue's offensiveness in deciding whether these excuses applied.
I personally find jury nullification as the ultimate form of democracy.
The reaction from the right wing government and its supporters was barely short of apoplexy, followed by promises to appeal the verdict and change the law to remove this as an option for juries. (So far I don't believe any such legal changes have been made.)
Jury nullification is one of the strengths of the jury system, allowing a representation of the public decide if an act was truly criminal, and should be protected, otherwise it's just 12 people following a decision tree and no better than trial by judge.
[1] https://www.theguardian.com/uk-news/2022/jan/05/four-cleared...