The phone hacking threat to Cameron.
Likewise, that NI today has been at pains to point out the amazing coincidence by which Brooks, then Wade was absent from the NotW offices both at the time Milly Dowler's phone was hacked and while the search was going on for Holly Wells and Jessica Chapman, putting the blame squarely on her deputy at the time Coulson has been an indication of just how terrified they now are at the potential implications, not just for Brooks, but for James Murdoch also. As Tom Watson today pointed out in the Commons during the emergency debate on the allegations, it was the heir apparent who signed off on the settlement with Gordon Taylor, the one Nick Davies got wind of and which restarted the whole affair two years ago. No wonder then that Daddy today gave Brooks his full backing to carry on the investigation into herself; she might have become "family" as it were, but if Brooks goes then so also must sonny boy.
Neither Brooks or junior face a potentially imminent knock on the door from Inspector Knacker though. Coulson has another reason to fear he might soon be visited by the Met's better late than never division. Having given evidence to the Tommy Sheridan perjury trial where he completely denied having any sort of relationship at all with Glenn Mulcaire, he also denied there was a "culture of phone hacking at the NotW", something that it's safe to say is now looking just ever so slightly shaky. If either NI themselves or the Met's latest investigation should come across something that suggests Coulson did indeed know about Mulcaire beyond his consultancy cover story, then he could well find himself following in the footsteps of such luminaries as Jeffrey Archer and Jonathan Aitken. While Coulson resigned as Cameron's chief aide not long after giving evidence, stating that he couldn't continue in the position while his old job still hung over him, it's not overly dramatic to suggest that should Coulson go down, he could take Cameron with him. You after all employ a spin doctor to tell lies for you; telling them under oath is taking it a little too far.