Lord McAlpine declared war on Sally Bercow over her alleged sex abuse smears by dropping all other libel cases to focus on suing the media personality.
McAlpine announced the move during his ongoing legal battle against social network users, who spread unfounded rumours online that he was part of a paedophile ring.
Retired McAlpine became the subject of frenzied speculation when MP Tom Watson described a "powerful paedophile network with ties to Downing Street" during Prime Minister's Questions.
McAlpine launched libel proceedings against a swathe of organisations and individuals. But today he dropped actions against all Twitter users with fewer than 500 followers.
This means the full focus of his lawyers will now turn to Bercow, who waded in to the speculation when it was at its height by tweeting: "Why is Lord McAlpine trending? *innocent face*"
As the backlash against her began, Bercow sent another tweet which read: "Final on McAlpine: am VERY sorry for inadvertently fanning flames. But I tweet as me, forgetting that to some of u I am Mrs bloody Speaker."
McAlpine said he was "consigned to lowest depths of hell" by rumour and innuendo about him.
Announcing his decision to drop thousands of libel actions, McAlpine said: "Whilst I reached a settlement last year with both the BBC and ITV, I would like to now draw this unfortunate episode, forced into my life, to a close."
"I have dropped all claims against those tweeters with less than 500 followers, in return for a very modest donation to BBC Children In Need, which funds 2,600 projects supporting disadvantaged children and young people in the UK.
"I have requested that my lawyers, RMPI LLP, focus on the action against Sally Bercow and that damages arising from this are donated to a charity of her choice. I am not intending to make any further comment on this matter."
Bercow's tweet was seen by her army of more than 60,000 followers and retweeted many times. Formerly a prolific Twitter user, Bercow has shut down her account.
The paedophile storm saw several public figures, including journalists, blunder by citing McApline. Guardian columnist George Monbiot issued a grovelling apology for claims made by him on Twitter against McAlpine.
Breakfast television host Philip Schofield was censured by ITV bosses for handing Prime Minister David Cameron live on air a list of names gleaned from a brief internet search.