PurpleStrawberry - that was my dh's response as well.
If you read the full transcript of Hugh grant's taped conversation with the ex NOTW hack he quotes the latter as saying the reason so many tory MPs resigned in the early 90s is because the papers had most of them over a barrell with secret recordings of shifty stuff they'd been up to. I have no doubt that the same is true of current politicians, not just Tory but Labour too.
So it would appear that no MP is willing to really take this on because of what might be revealed about them. It is no less tham blackmail as far as I can see.
Peetle - good point about Cable.