The Home Secretary, Jack Straw, said the Government had taken the step in the interests of national security. He said the disclosures had "already caused serious harm".
Mail on Sunday editor Jonathan Holborow condemned the decision to seek a High Court injunction, saying it was a "serious assault" on press freedom.
He told Sky News: "The director general of MI5 has used this attitude that lives of his employees may be at risk to cover up the embarrassment that our articles last week caused him."
Former MI5 agent David Shayler's girlfriend joined him in criticising the security service and its director general, Stephen Lander. Annie Machon, a 29-year-old former MI5 intelligence officer, claims in today's Mail on Sunday that the service is riddled with discontent. She also details how MI5 wasted tens of thousands of pounds monitoring Socialist Workers' Party annual meetings in Skegness.
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