A spokesman for the legal firm Carter Ruck has told ITV News: 'Lord McAlpine has issued and served proceedings for libel against Sally Bercow and we are representing her.
"He has put in a claim limited to £50,000."
The peer alleges that the Commons Speaker's wife posted a libellous tweet that wrongly linked him to child abuse.
More top news
A hacker group who claimed to be behind a cyber attack on Sony Pictures have posted a message online apparently mocking the FBI.
The returns of Benedict Cumberbatch's detective and the X Factor judge were among 2014's most tweeted TV moments in a billion conversations.
A family has issued an appeal to help find their missing pet turkey - in case he gets gobbled up as someone's Christmas dinner.