By Laura Kuenssberg
BBC political correspondent
The PM has tried to distance himself from his former close adviser
Prime Minister Gordon Brown has expressed his regret to those mentioned in e-mails containing false and lurid allegations penned by his former close adviser Damian McBride.
So, is that it?
Three days after sources close to Number 10 tried to contend the McBride e-mails were just a bit of banter between old mates, the prime minister has had to distance himself publicly from the lurid emails, sent from right under his nose.
Gordon Brown has made it known that he's writing privately to the Conservatives who were smeared in the messages - David Cameron, George Osborne, and the MP Nadine Dorries.
But although he has said the scandal is a "matter of great regret", he has stopped short of actually saying sorry - allowing the Tories to keep hammering away until he does.
One can only imagine how furious the prime minister was being forced to take up his pen to write such a note.
He emphasised again on Monday evening that no-one else in Downing Street or any other minister knew anything about what was going on.
David Cameron has welcomed Mr Brown's move, saying it shows he has finally accepted how serious the situation was. But the Tories have not let it drop.
None other than Tory grandee Lord Heseltine says that prime ministers know everything that goes on in Downing Street, and that regret about this affair has only been expressed because the perpetrators got caught.
In another attempt to close the story down, the PM has asked the Cabinet Secretary, Sir Gus O'Donnell, to tighten up the rules on what special advisers are and are not allowed to do.
But before this affair, the rules were already clear that advisers should avoid personal attacks.
A crackdown on the code of conduct will not shift the stain of the e-mail affair, even though such activity will now be an automatic sacking offence.
And still there are Labour voices calling for more.
Former deputy prime minister John Prescott says that Derek Draper - who received the e-mails - should be cut loose from his unpaid, self styled "unofficial" role as new media adviser to Labour.
Mr Prescott has written on the Labour website, Go Fourth: "I understand one man has left his job at No 10 - and quite rightly."
No response so far from Mr Draper - who has already exited Number 10 - on whether he'll follow Damian McBride and sever his links completely but it is hard to see how either man could make any public return to politics.
It is equally difficult to see how Downing Street will be able to shake off the damage caused by the backroom activities of one of the PM's closest political confidants.