Rebekah Brooks, former editor of the News of the World and the Sun, is giving evidence at the Leveson inquiry today.
Barry Batchelor, PA Wire
Mrs Brooks resigned from her executive role at the media company News International in July 2011 during the phone-hacking scandal.
She had been editor at the News of the World while the illegal hacking of mobile phones was allegedly taking place.
Two days after her resignation she was arrested on suspicion of conspiring to intercept communications and on suspicion of making corrupt payments to public officials.
She was arrested again in March 2012 on suspicion of conspiracy to pervert the course of justice.
The Leveson inquiry, which is investigating the standards and behaviour of the UK media, is likely to focus on Rebekah Brooks' relationship with politicians and her former employers News International.
The inquiry will not be able to ask any questions relating to the criminal investigations under which Mrs Brooks has been arrested: Operation Weeting, the Metropolitan Police's phone-hacking probe, and Operation Elveden, the investigation into illicit payments to police officers.
Instead questions will be asked about her close relationship with senior politicians, including the current prime minister David Cameron and his predecessors Tony Blair and David Cameron.
While editor of the Sun and the News of the World, Brooks made sure her newspapers backed Tony Blair at three general elections.
She was once a guest of Gordon Brown as a pyjama party held at the prime minister's country residence.
In 2008 she was loaned a retired horse by the Metropolitan Police, which she kept on her Oxfordshire farm and which was subsequently ridden by David Cameron.
Mrs Brooks' wedding to former racehorse trainer and author Charlie Brooks in 2009 was attended by both Gordon Brown and David Cameron.
In December 2010 a dinner party at the Brooks' house was attended by David Cameron, by now prime minister, and James Murdoch, chairman and chief executive of News Corporation in Europe and Asia.
Mr Cameron is said to have sent text messages to Mrs Brooks expressing sympathy when she was forced to resign from News International in 2011.
Some or all of these events are likely to be the subject of questions at today's hearings of the Leveson inquiry.
Mrs Brooks is expected to spend the whole day giving evidence.