Andrew Mitchell's lawyers sent The Sun a "letter before action" last month, putting it on notice that the Conservative MP intended to sue.
At the time, his lawyer Graham Atkins told The Guardian: "We are seeking damages, an apology, an undertaking that the words complained of are not repeated, and costs."
The newspaper was the first to break the story of Mr Mitchell's row with the officers at Downing Street, which became known as the "Plebgate" scandal.
More top news
Labour leader says the UK "should not be afraid of debt or borrowing" as he urges the government to "stop dithering" and start investing.
A fundraising page for a Westminster terror attack victim has been taken over by JustGiving amid fears it was set up by a fraudster.
ITV News rounds up the best pictures of the day as campaigners make a final stand before Theresa May triggers Brexit on Wednesday.