 a group of climate change activists who plotted to shut down the UK's second largest power station have been invited to launch appeals against their convictions.  The 20 protesters received letters from the Director Of Public Prosecutions after a review of the activities of an undercover police officer surrounding planned demonstrations at Ratcliffe-on-Soar power station.  The group, convicted of aggravated trespass, were among more than 100 people arrested when police raided the Iona School in Sneinton, Nottingham, on 13 april last year. Keir Starmer QC has invited the protesters to appeal against the convictions after a review into the "non-disclosure of material" relating to the activities of the undercover officer. The protesters were convicted at Nottingham Crown Court in December.  In February, the head of the association of Chief Police Officers (acpo) said undercover policing operations should have to be authorised in advance by a judge. Sir Hugh Orde, acpo president, said the change was needed to restore public confidence after concerns about the role played by ex-Metropolitan Police constable Mark Kennedy, who spent seven years posing as an environmental activist.