If a defendant had an honest and reasonable mistake of affairs, if they existed, would make an accused’s actions innocent when in another situation they would constitute an offence. The act would not have been done with a guilty mind.
The defendant has the onus of providing evidence to raise the mistake of fact. However it will be up to the prosecution to negative the defendant’s belief.
An example where the defence of honest and reasonable mistake of fact can be used is where a person has been charged whilst their licence was suspended. If they had a honest and reasonable belief that their licence was valid at the time and this can be shown through evidence then their actions could be seen as honest and reasonable in the circumstances and thus should not be found guilty of the offence.
This defence needs to aspects honest and reasonableness. Because of this it is often difficult to overcome both aspects.