Depends on what is leaked and to whom.
Civil Servants do have a duty of confidentiality as well as the Official Secrets Act to consider but then there is the matter of conscience and of course the public good.
Nulabour and in particular Gordon Brown made their names using leaks from Civil Servants ~ whilst some leakers may have been found and punished by the Civil Service (and that is a risk they accept) no MPs were arrested, nor were MPs offices and homes searched. The Wilson Doctrine applies ~ and Blair/Brown confirmed that "protection" for MPs.
As others have said Mandleson's prints are all over this. Brown is very good at saying one thing and interpreting it to suit himself later whilst using the likes of Mandy, Ed Balls and Charlie Wheelan to do the dirty work.