The Metropolitan police is to assess whether criminal prosecutions can be brought over Twitter messages that linked Lord McAlpine with allegations of child sex abuse.
Lawyers for the Tory peer will meet Scotland Yard detectives on Wednesday to begin a scoping exercise into the allegations, the Met confirmed.
Scotland Yard said in a statement: "We have not received an allegation of crime at this time, however, we can confirm we will be meeting with interested parties to start the process of scoping whether any offence has taken place. It is far too early to say whether any criminal investigation will follow."
Lawyers for McAlpine said they had identified up to 10,000 allegedly defamatory tweets about the former Tory party treasurer.
They announced plans to sue Twitter users and broadcasters, including the BBC and ITV, for libel following the inaccurate Newsnight report into child sex abuse on 2 November.
Twitter users could be prosecuted under the Malicious Communications Act if their messages are found to be grossly offensive.
The prospect of criminal convictions for allegedly defamatory Twitter messages is likely to raise the temperature on the debate over free speech online. Several users of Twitter and Facebook have been prosecuted – and some jailed – in the past year over offensive messages.
Separately, a spokeswoman confirmed that McAlpine hoped to settle his libel battle with ITV on Wednesday. He sued the broadcaster over Phillip Schofield's on-air blunder that linked several Conservative politicians with allegations of child sex abuse.
Solicitors for the Tory peer have entered a third day of negotiations with lawyers for the broadcaster over the terms of the six-figure libel payout.
A spokeswoman said on Wednesday: "Lord McAlpine is hoping to reach a settlement with ITV today."
ITV's bill is likely to be significantly greater than the £185,000 paid out by the BBC over its erroneous Newsnight report last week.
McAlpine's lawyers and PR firm have refused to be drawn on speculation he could demand as much as £500,000 from ITV over Schofield's onscreen ambush during an interview with the prime minister. ITV had not responded to a request for comment.
The former Tory party treasurer on Tuesday night said he would donate compensation received from Twitter users to BBC Children in Need.
He has asked those who defamed him on the social network to donate a "sensible and modest amount" to the charity to mitigate any libel action.
McAlpine's lawyers said in a statement: "The fixed donation amount is yet to be assessed. However, this will be to Lord McAlpine's charity of choice, BBC Children in Need, and will be in addition to an administration fee.
"Given the large amount of information that continues to be disseminated, the band for which the charity payment will be settled shall be when Lord McAlpine has a full understanding of this material.
"The donation is intended for tweeters with fewer than 500 followers, but those with larger numbers of followers are still encouraged to identify themselves and offer their formal apologies at this stage."
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