British Prime Minister Gordon Brown insisted yesterday that no government ministers were involved in efforts by one of his former top aides to spread unfounded allegations about opposition lawmakers.

As he sought to draw a line under a highly embarrassing affair, Mr Brown said he had personally written to Conservative MPs targeted in "obscene" e-mails written by Damian McBride, the head of strategic planning in Mr Brown's office who was forced to quit on Saturday after the e-mails were leaked.

He did not explicitly apologise but said: "Any activity such as this that affects the reputation of our politics is a matter of great regret to me".

In a letter to the head of the civil service, Gus O'Donnell, Mr Brown wrote: "I am assured that no minister and no political adviser other than the person involved had any knowledge of or involvement in these private e-mails".

He added that he had "written personally to all those who were subject to these unsubstantiated claims".

Mr Brown also called for the rules governing special advisers such as Mr McBride to be tightened.

"The preparation or dissemination of inappropriate material or personal attacks have no part to play in the job of being a special adviser, just as it has no part to play in the conduct of all our public life," he wrote.