Sir Jeremy Heywood, the Cabinet Secretary, was criticised by MPs after admitting he didn't probe the word 'pleb' in his investigation of the events that led to the resignation of former Tory Chief Whip Andrew Mitchell.
ITV News Correspondent Juliet Bremner reports:
Britain's most senior police officer has promised a "ruthless" investigation into an alleged conspiracy against Andrew Mitchell.
Andrew Mitchell has written a piece in which he has accused the police of trying to destroy his career in a smear campaign.
Police investigating the row involving Andrew Mitchell have arrested a second man today. See how the "plebgate" events unfolded.