Sir Anthony O'Reilly spent €18.6 million (£14.6 million) shoring up his position in Indepedent News & Media on a day when the newspaper group accused the rebel investor Denis O'Brien of behaving as a “dissident shareholder”.

The share buying took the chief executive's stake up to 27.94 per cent - ahead of Mr O'Brien's 22 per cent - as executives at the company behind The Independent newspaper titles went on the offensive in an attempt to put their rival under pressure. Independent News & Media said that Mr O'Brien's “comments and actions regarding IN&M, its board, management, strategy and governance, are designed to destabilise”. He has called for the sale of the loss-making Independent in London and demanded that Sir Anthony quit because he is too old.

Company bosses also released quotes from a letter written by Mr O'Brien in an attempt to flush out the motivation behind the telecoms entrepreneur's long pattern of share buying, which has made him the second largest shareholder in the newspaper group. The letter, written by Mr O'Brien in July 2003, included allegations that Irish newspapers owned by the company “had spent the last seven years trying to destroy my reputation” and that he was “waiting for the appropriate time to rectify the damage”.

Coverage of Mr O'Brien has focused on the decade-long Moriarty Tribunal, which is examining whether the businessman was awarded the second mobile phone licence in the country after bribing a government minister.

Mr O'Brien hit back in a statement that described the accusations as a “highly personal and unwarranted attack” that “appears to be designed to deflect attention from the company's disappointing stock performance”.

This week shares hit a four-year low but rallied 8.7 per cent to €1.87 after the company reported upbeat results.

Independent News & Media executives have become alarmed about Mr O'Brien's share buying in recent weeks when directors could not invest because the company was in a closed period, and his calls for asset sell-offs, which they say is unsettling employees.

The Independent, the UK's fourth-ranked quality daily, continued to lose money last year although its losses reduced by £1 million. “The Independent remains a core part of what we are as a group,” Gavin O'Reilly, the chief operating officer of the company, said yesterday. Helped by profits at the Belfast Telegraph, profits in the UK were €15.5 million, up 8.4 per cent in the year. Pre-tax profits for the whole group, which includes newspapers in Ireland, South Africa, and interests in Australia and New Zealand, were off 0.4 per cent at €248.4 million.

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