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
Jeremy Corbyn is writing to the Parliamentary Labour Party to say he cannot back airstrikes on Syria, ITV News understands.
Rows of students stood and turned their backs before filing out of the lecture theatre.
Two-sub machine guns and ammunition were found in a police raid on traveller sites across Northern England