McDonald's also employed up to seven private detectives to gather information on the pair. The revelations came to light during the court action between the burger chain and the "McLibel Two", Helen Steel and Dave Morris.
The hamburger chain alleges that in the late Eighties the pair distributed a leaflet accusing McDonald's of producing food linked to heart disease, diabetes and cancer. The leaflet also accuses the fast-food outlet of abusing animals, its workers and the environment.
The pair, who are defending themselves against the $26bn corporation, deny libel, arguing that the leaflet paints an accurate picture of the company's activities. The case, which is now in its 23rd month and is expected to last at least until the end of the year, is being heard without a jury.
Sydney Nicholson, McDonald's vice president in the United Kingdom and former head of security, told the High Court that Special Branch officers supplied information to the company about environmentalists believed to be handing out the leaflet.
In 1989, officers from the Animal Rights National Index, which gathers information on animal-liberation activists for Special Branch, identified protesters outside the company's headquarters. At least two of the campaigners were subsequently issued with libel writs by the burger chain.
Mr Nicholson told the court that Special Branch had said they considered the two environmentalists to be of "very little importance". What they were interested in was the possible connections with the animal liberation groups, and they did not indicate either of the two were involved in that, he said.
Mr Nicholson said he did not know if Special Branch had held any other meetings with the burger company's private security agents because he never questioned them about their sources. "All the [McDonald's] security department have many, many contacts in the police service, they are all ex-policemen; I would not ask them who their contacts were," he said.
He said that he would use police contacts for information. "If I wanted to know something about someone I would almost certainly make contact with the local crimes beat officer, the local CID officer, the local collator," he said.
McDonald's also used two detective agencies with at least seven undercover agents to monitor activists from London Greenpeace, which produced the leaflet and to which Ms Steel and Mr Morris belong. The organisation has no connection with Greenpeace International.
London Greenpeace meetings were frequently attended by fewer than 10 people. Mr Nicholson said he did not believe the number of agents monitoring the group and attending meetings would affect the direction of the organisation.
Ms Steel claimed that at one meeting in 1990, four people attended, three of whom were undercover agents from two different private investigation agencies working for McDonald's.
Mr Nicholson said he "had no idea" if three of the four were acting for McDonald's. "If they did, then that was the object of me using two agencies," he added.
Agents acting for McDonaId's also took letters belonging to the group. Mr Nicholson told the court that he gave categorical instructions for the agents to do "nothing illegal and nothing improper". But, he added: "People do make mistakes."
A spokeswoman for Scotland Yard denied that Special Branch regularly supplied information about suspected political, animal rights or environmental activists to companies. They would, however, tell them if they believed an organisation posed a threat to them."It is not the practice of the Metropolitan Police to provide lists of activists and we are unaware of any instances where that has happened," she added.