The director of public prosecutions, Kier Starmer, has advised 20 climate activists to appeal against their convictions.
They were convicted of plotting to break into a power station in 2009.
But the convictions took place while undercover police officer Mark Kennedy had infiltrated the group.
Kennedy was said to have played a key role in orchestrating the plan.
The police are also suspected of suppressing evidence because of what it may reveal about Kennedy’s involvement.