O'Brien, who has been building up his holding since April last year, is openly critical of Sir Anthony O'Reilly, IN&M's chief executive and largest shareholder. O'Brien has called for the company to sell off its loss-making flagship national newspaper titles.
The Week: City news - O'Brien raises IN&M stake
Denis O'Brien, the Irish media tycoon, has increased his stake in Independent News & Media, the publisher of The Independent and Independent on Sunday, from 18.05 per cent to 19.35 per cent.