An undercover police officer has admitted that he spied on Keir Starmer while he was a radical barrister, a public inquiry has heard. The police spy has said that he accessed confidential details of the legal advice that Starmer was giving to two environmentalist campaigners in the well-known McLibel case in the early 1990s. The contents of the advice were then relayed by the spy to his managers in a covert Scotland Yard unit, the inquiry was told on Tuesday. At the time, the prime minister was building a reputation as a civil liberties barrister championing causes as diverse as striking trade unionists to prisoners who had been sentenced to death around the world. One of the cases concerned a pair of environmental campaigners, Helen Steel and Dave Morris, who – in a David v Goliath case – were sued for libel by McDonald’s over a leaflet they had distributed criticising the company’s practices. Confronted with the legal might of the US fast food giant, the pair turned to Starmer who gave them free advice on how to defend themselves. The impecunious pair could not afford lawyers to represent them in what turned out to be the longest civil trial in English history. The advice Starmer provided for the McLibel two has played an important part in his life and his subsequent political career. It was cited in his leadership bid in 2020, with his campaign launch video describing how “for 10 years he defended Helen Steel and David Morris when they were sued for libel by McDonald’s. They fought all the way and won.” Now the covert monitoring of the McLibel pair, including Starmer’s legal help, will be scrutinised in the coming months at the inquiry. It will also hear allegations that Starmer’s legal advice was shared with McDonald’s to help the corporation win the case. The public inquiry is examining how police deployed about 139 undercover officers to spy on more than 1,000 political groups between 1968 and at least 2010. One was John Dines who infiltrated anarchist and environmental groups between 1987 and 1991. During his deployment, he formed a two-year intimate relationship with Steel, but concealed from her the fact that he was employed by the Special Demonstration Squad (SDS), a covert Scotland Yard unit, to spy on her and her circle of campaigners. She eventually pieced together disparate clues to expose him after he disappeared without a trace. On Tuesday, Morris gave evidence to the inquiry in which he quoted from a witness statement that has been made by Dines. He quoted Dines as saying : “It is accurate to say that I was by the side of Helen Steel and Dave Morris in 1991 and relaying the legal advice back to my bosses in the SDS.” Morris said that the only lawyer giving them legal advice at that time was Starmer. Dines’s witness statement will be published at a later date by the inquiry. Morris told the inquiry: “Dines was getting details of our confidential legal advice and strategy following the private legal meetings Helen and I held with lawyer Keir Starmer.” He said this was a clear breach of the longstanding legal rule that lawyers and their clients can debate tactics within a protected ring of confidentiality. Morris said he discussed Starmer’s advice and the legal case when he visited Steel who was at that time living with Dines. He cited evidence showing that the police secretly passed information about the campaigners to McDonald’s. He alleged the police secretly shared Starmer’s confidential legal advice and other information with McDonald’s which gave the corporation an advantage in the legal battle. Those who have worked with Starmer say his time as director of public prosecutions between 2008 and 2013 knocked some of the leftwing campaigning zeal out of him. One former colleague told the Guardian last year: “When he was very young would say he was extremely leftwing … he had all those leftwing shibboleths, which he has reconsidered since he became a public servant.” The McLibel case was widely seen as a public relations disaster for McDonald’s. It exposed damaging stories about its business and the quality of food it was selling. It was also seen as a heavy-handed way of stifling criticism. In 1997, a high court judge ordered Steel and Morris to pay £60,000 in damages for libelling the corporation in what was a partial victory for McDonald’s. But the pair never paid. Downing Street did not respond to a request to comment.