A politician who complains about the media is like a sailor complaining about the sea. Coping with choppy waters is part of the job.

So it’s not often they call in the lawyers to deal with a dispute with the press. In Tom Watson’s case, however, it’s not clear what option he had.

The exposure of a plot to spread smears about Conservative MPs has already destroyed the career of one Number 10 official. Claims that Mr Watson was part of that plot threaten to hinder or end the ministerial rise of the Black Country MP - even though they are unjustified. We say this with some confidence because the source of the accusation, the Conservative activist and blogger Iain Dale, has said so himself and admitted he was mistaken.

But when mud is thrown it tends to stick, and the claim has been repeated in many parts of the media. Conservatives appear keen to gain a scalp, and Mr Watson is their target.

While it is unfair to lay the blame on him, the more general Conservative outrage at what seems to have been going on in Downing Street is entirely justified. It is reasonable to ask, as Tories have done, that spin-doctor Damian McBride’s e-mail accounts are examined to see who he was communicating with.

He was working in Number 10 and receiving taxpayers’ money. Furthermore, Mr McBride was no junior official. Rather, he was a long-standing and close aide of the Prime Minister.

Gordon Brown has effectively disowned him, giving the impression that he acted alone and without authorisation. Well, that remains to be seen. If Mr Brown wants to refute claims that the planned smear campaign represents the “dark side” of his government, he must ensure there are no secrets and Mr McBride’s actions are made entirely public.