Saturday, September 18, 1999 Published at 16:51 GMT 17:51 UK
Home Office defends spy secrecy
Dr Pearson gave information about Nato staff to the Stasi
The Home Office has said it is "wholly unrealistic" to expect spying investigations to be made public, after a third Briton was uncovered as a Cold War agent.
It revealed that he spied for 12 years for East Germany's notorious Stasi secret police.
His Conservative counterpart Ann Widdecombe said: "Every day there has been another development to this farce.
"Is Jack Straw going to finally make a statement or is he going to let the press do his job for him? That is the question."
None of the three spies uncovered in the last week have been prosecuted.
Hull University also says Dr Pearson is free to return to work when the new academic year starts.
The statement added that it would be "grossly irresponsible" to make the inquiries public as "such disclosure could very seriously compromise the work of the agencies, which, to be effective, have to a large degree to remain secret".
The Home Office said Mr Straw had been briefed about the case, by MI5, only last weekend.
It praised the work of the security services, under scrutiny since details of files brought to Britain by KGB officer Colonel Vasili Mitrokhin were revealed.
The Home Office added: "The material in the Mitrokhin archive demonstrates that because of the actions taken in the 1970s, the KGB was less successful in this country than in others."
A former KGB agent has also claimed this week two Labour MPs, Tom Driberg and Raymond Fletcher - both now dead - had been spies.
Dr Pearson was recruited by the East German secret police, the Stasi, in 1977 and served as a "long-term penetration agent" for 12 years.
When the German Democratic Republic (GDR) collapsed in 1989 hundreds of files were destroyed by the Stasi.
But four files survived, including one which contained information on a British Stasi agent codenamed "Armin".
He has now been revealed as Dr Pearson, a 44-year-old lecturer who is married with two children.
The Spying Game is on BBC Two at 8pm on Sunday 19 September.