British spies were compromised by FBI traitor Hanssen

Spying operations and agents belonging to Britain's intelligence services, MI6 and MI5, have been compromised after their details were divulged to the Russians by a notorious FBI traitor.

The Independent has learnt that a number of counter-espionage operations have had to be altered and may be scrapped as a result of information that was leaked by Robert Hanssen during a spying career that stretched over three decades and caused unparalleled damage.

Both MI5 and MI6 are carrying out a full review of the harm inflicted on their operation both at home and abroad after initial findings concluded that "significant damage" had been caused by Hanssen.

Hanssen, whose double dealing was only halted last year, is due to be sentenced later today to life imprisonment without the option of parole when he appears before a federal court in Alexandria, Virginia. He had faced the possibility of the death sentence. He is expected to make a statement to the court prior to sentencing in which he will express regret for his actions.

Hanssen, 57, a senior counter-intelligence agent for the FBI, was involved in a number of joint operations involving the American intelligence service and MI6, which deals with issues abroad, and MI5, which concentrates on threats to British security. It is understood that Hanssen had high-level access to information about a number of joint operations involving Britain.

The betrayal of any of the details, including the names of spies, to his Soviet and later Russian masters, has the potential to be extremely harmful. A source confirmed Hanssen had caused "damage" to their operations, particularly involving the Russians, and that as a result new security measures had been implemented. It is not known whether any agents have been withdrawn from Russia.

The Security Service, MI5's counter-espionage section, and MI6, the Secret Intelligence Service, are assessing the damage caused by Hanssen, as is America's intelligence community. Even a small degree of penetration of the agency's security is considered to be very serious. Most of the joint British and American operations in the former Soviet countries involved MI6, but MI5 also took part. The Security Service also worked alongside the FBI to counter Russian espionage in Britain.

An initial assessment concluded, however, that among the secrets betrayed by the married, father-of-six, were: the US continuity of government plan, which details what provisions are in place to protect the President and key members of government in the event of a nuclear attack; the identity of at least nine Soviet officials recruited to spy for the US, several of whom were subsequently executed; the national intelligence programme, which detailed what the intelligence community intended to do for an entire year; a number of individual projects costing hundreds of millions of dollars, including the existence of a secret eavesdropping tunnel dug beneath the Soviet embassy in Washington.

In a document placed before the court earlier this week, the US Attorney Paul McNulty said on behalf of the American government: "Hanssen's brazen and reckless misconduct, its surpassing evil, is almost beyond comprehension. Using the very tools he acquired as [with the] FBI he covertly and clandestinely provided the Soviet Union and then the Russians information of incalculable significance, extraordinary breadth and exceptionally grave sensitivity.

"He did so knowing that his disclosures could – and ultimately did – get people killed and imprisoned, and he did so knowing that they placed in jeopardy the safety and the security of our entire nation. That we did not lose the Cold War ought to blind no one to the fact that Robert Hanssen, for his own selfish reasons, placed every American citizen in harm's way."

Robert Vise, a reporter for the Washington Post and author of The Bureau and the Mole, an exhaustive account of Hanssen's treachery, said: "Robert Hanssen was the most prolific and dangerous spy in American history."

What has not been clear until now, however, is the damage inflicted on the operations of America's intelligence allies, including Britain, Australia and Canada, all of which were forced to launch damage limitation exercises once Hanssen's treachery was revealed.

One of the most staggering things about the Hanssen case was the range of material to which he had access – partly as a result of his expertise with computer information systems and partly because of insufficient internal security checks at the FBI. It is known that he betrayed secrets not just from the FBI but from the CIA, the Pentagon, the White House and the National Security Agency.

Hanssen's lawyer, Plato Cacheris, said his client expected to be sentenced to life imprisonment – a deal hammered out with prosecutors in exchange for his co-operation in listing the material he had revealed. "Given the alternative I would say he views [the expected sentence] rather favourably," he said.