Dr Gwyneth Edwards, who taught at Loughborough University, is identified as an agent in Stasi files which have been obtained by the UK security services.
She is the fourth living Briton to have been accused of spying in the past week.
The existence of the Stasi ring has been exposed by American intelligence officers who have now handed all their information to the British secret services.
It centred around Dr Robin Pearson, a senior lecturer in economic and social history at Hull University who is said to have worked for the East German secret police for 12 years.
Last night the historian Professor David Childs, who has had access to the East German secret police documents, confirmed that Dr Edwards, a modern languages expert, was named in the files.
"The East Germans liked to recruit foreign academics because they often had access to research information," he said. "They could get into government service or spy on other academics."
Dr Edwards is alleged to have been part of a 20-strong spy ring recruited by the East Germans. It is said that one of her roles was to report back to her controllers on any anti-Communist comments made by visiting German academics. It was not possible to contact her last night.
Dr Pearson, codenamed "Armin", was allegedly recruited while studying in Leipzig as part of his German history degree at Edinburgh University.
A Home Office spokesman said yesterday that Dr Pearson had been interviewed by the security services in 1994 but it was decided that there was "no usable evidence" against him.
His Stasi handler, Berhart Kartheus, told the BBC2 series The Spying Game, which starts tonight, that the East Germans successfully recruited one in 10 of the British exchange students they approached during the Cold War. Experts estimate that this means there are likely to be up to 20 still living in the UK.
A massive undercover investigation is now under way by MI5 and MI6, Britain's internal and external security services, to track down and prosecute up to 30 Britons suspected of handing secrets to the Eastern bloc before the fall of the Berlin Wall. They are thought to include serving police officers, who have been identified by the former Scotland Yard detective and self-confessed agent John Symonds.
The operation will fuel Opposition criticism of the Government's decision not to prosecute other agents who have recently been unmasked, including the great-grandmother Melita Norwood.
Up to 15 former KGB agents are also under investigation in a separate operation after being identified from the files brought out of Russia by the defector Colonel Vasili Mitrokhin.
Their names were deliberately withheld from the published version of his archive in order to stop them fleeing the country to escape prosecution. British intelligence officers are now interviewing other KGB defectors in an attempt to build up a case which will allow charges to be brought successfully.
Ann Widdecombe, shadow home secretary, demanded a full explanation from Jack Straw about the Government's failure to prosecute the alleged agents.
"We are only finding out about these things through press revelations," she said. "That will go on unless he actually makes a very clear statement saying how many, were there any very serious ones, what were the criteria used [in deciding on prosecutions] and were there any instances in which ministers should have known, under whatever administration, and didn't know."
The Home Office issued a statement saying that it would be impossible to disclose all the details of security service investigations. "In fulfilling its function of protecting national security, the Security Service has, over the years, carried out a great many investigations, including into allegations of espionage and hostile foreign intelligence activity," the statement said. "It is wholly unrealistic to believe that the fact that investigations have been carried out or the detail of them should routinely be made public. It would be grossly irresponsible as such disclosure could very seriously compromise the work of the agencies which, to be effective, have to large degree to remain secret."Reuse content