Director of Public Prosecutions Kier Starmer QC has told 20 people to appeal against convictions over a protest at Ratcliffe-on-Soar power station.

His letter comes after revelations that the protesters had been infiltrated by an undercover police officer.

Mr Starmer said the CPS had reviewed the safety of the convictions in 2010 amid allegations about the officer, former Pc Mark Kennedy.

The Court of Appeal should look at the cases as soon as possible, he added.

The 20 protesters contacted by Mr Starmer were convicted in December 2010 of conspiracy to commit aggravated trespass at the Nottinghamshire power station.

They were given community service orders and conditional discharges - and the judge accepted they were "decent men and women" motivated by their fear for the environment.

But a month later, the prosecution of a further six people collapsed when the CPS said that "previously unavailable material" had emerged that undermined the case.

The decision to drop the case came as it emerged that Mark Kennedy, who had infiltrated environmental groups, had offered to help the help the defence.

Following the collapse of the six cases, Mr Starmer asked senior barrister Clare Montgomery QC to review the prosecutions of the 20 who had already been convicted.

In a statement on Monday, Mr Starmer said: "I instructed Ms Montgomery to review the safety of the convictions of the individuals convicted at Nottingham Crown Court on 14 December 2010 in light of non-disclosure of material relating to the activities of an undercover police officer.

"Ms Montgomery has now completed her review and, having carefully considered her conclusions, I believe that the safety of the convictions should be considered by the Court of Appeal as soon as possible.

"The prosecution cannot lodge an appeal to the Court of Appeal save in very limited circumstances, which are not met here, and in my letter I have invited the defence to lodge an appeal and to include the issue of non-disclosure of material relating to the activities of an undercover police officer in any grounds of appeal.

"I have also indicated that the CPS will assist in any steps necessary to expedite the appeal."

Two reviews

There are two separate reviews into the affair. The first, by the Independent Police Complaints Commission, is looking at the alleged failure of Nottinghamshire Police to disclose material to the defence. The second, by the Inspectorate of Constabulary, is looking at the wider question of how undercover officers operate.

But Mr Starmer said that despite these reviews, the only proper course of action would be to invite appeals now.

He said: "It would be wrong if, having reached this conclusion [about the convictions], I waited until the reviews were completed before contacting the defence about a possible appeal."