'Friends of David Cameron' have called the accusations pretty low rent, they've not denied them though.
So now it's OK for a party leader to lie to Parliament.
On a serious note, surely Cameron has to sue otherwise the accusations, whether true or not, will dog him for the rest of his career.
Look at Cliff Richard, The Elm Guest house rumours have been following him for years, unless of course there is worse that would come out in court