TWENTY-NINE people convicted of offences after a climate change protest at Drax Power Station have had their convictions quashed by leading judges.

The Court of Appeal decision came after an announcement in 2012 by the then director of public prosecutions Keir Starmer that there were concerns about the safety of convictions which followed the protest at the power station near Selby in 2008.

The convictions were overturned today by the Lord Chief Justice Lord Thomas, Mr Justice Simon and Mr Justice Irwin because of the failure to disclose the fact that a Metropolitan Police officer, Mark Kennedy, had been working undercover during the protests.

Lord Thomas said: "There was a complete and total failure, for reasons which remain unclear, to make a disclosure fundamental to the defence.

"In those circumstances, this court has no alternative but to quash the convictions."

Outside court, Beth Stratford, speaking on behalf of the 29, said: "We are pleased because this shines a light on the underhand tactics of the police and the Crown Prosecution Service (CPS) in their policing of political movements. It underlines further the need for public independent inquiry into the use of political policing."

The actions of Kennedy, who spent seven years posing as Mark "Flash" Stone, had led to the collapse in 2011 of the case against six protesters accused of planning to invade the coal-fired Ratcliffe-on-Soar power station in Nottinghamshire and led to a review of police undercover tactics.

At Drax, the environmental campaigners ambushed a freight train as it took fuel to the largest coal-fired power station in Europe.

Participants in the non-violent protest were sentenced at Leeds Crown Court in 2009 for obstructing the railway.

The court heard how the train was stopped by two men posing as Network Rail staff, wearing orange jackets and hard hats, who held up a red flag.

Moments later, the train and a nearby bridge were scaled by the protesters wearing white paper boiler suits and carrying banners.

The protest lasted 16 hours, causing delays to numerous freight and passenger services and the clean-up operation cost Network Rail nearly £37,000.

Defendants told jurors they did not believe they were doing anything criminal because they were trying to prevent climate change.

Some were ordered to do 60 hours of unpaid work and others were given conditional discharges for 12 months.