THE first rumour to go swirling around Westminster after Alan Johnson's sudden resignation was that it was yet another case of a politician caught philandering.
The rumour was correct only in one limited sense. Alan Johnson resigned rather than have a sex scandal burst over his head while he was still in office -- but, unusually, he was sinned against, rather than the sinner.
Two tabloid newspapers had picked up a tip from the Metropolitan Police that there was an internal investigation under way into one of Mr Johnson's former close-protection officers, who had allegedly had an affair with Laura Johnson -- the wife of the man he was supposed to be protecting.
It is thought that the newspapers had been given the tip in exchange for a promise that they would not publish until the officer had been disciplined, in order not to put the police in an embarrassing position. Johnson's resignation forced the story out earlier than their informant had wanted.
Officially, nothing has been confirmed but the fact that the story has not been denied has given it credibility.
Paul Rice, a detective constable who was assigned to guard Mr Johnson when he was home secretary, was last night suspended amid the allegations.
In a statement, the Metropolitan Police said: "A Metropolitan Police Service Specialist Operations Police Constable has today been suspended from duty pending the outcome of the Directorate of Professional Standards investigation into allegations reported in the media regarding an inappropriate relationship.
"A thorough investigation is now under way. As the allegation is subject to investigation, we are not able to comment further at this stage."
Unofficially, a source at the Met had said earlier: "Everything will hinge on whether or not the relationship started while he was still part of Johnson's protection team and whether he was conducting the affair when he was on duty. If the answer is yes, then that is career-threatening. But if the relationship only started when he was no longer looking after Johnson, then I'm not sure it will be a problem."
His departure was met with real regret in Westminster where he was a popular figure, not least because of his background.
While it has become common for politicians to be found out cheating on their wives, Mr Johnson is the first to resign because of a sex scandal in which he was the aggrieved party.
A year ago, the North's political establishment was shocked by the revelation that Iris Robinson, wife of First Minister Peter Robinson, had an affair with a 19-year-old man.
Mr Johnson married Laura Jane Patient in 1991 and the couple have a 10-year-old son. According to reports, their marriage is now over.