Diamond's shift from defiance to defeat So what changed? Less than 24 hours before the resignation of Bob Diamond as chief executive of Barclays, the bank's chairman was insisting Mr Diamond had the full backing of the board and was the best person to run the bank. Marcus Agius was confident that his decision to step down as chairman would be enough to stem the political pressure on the bank following its £290m fine last week for manipulating the interbank lending rate Libor. He and Mr Diamond were preparing for their much-anticipated appearances in front of the Treasury select committee MPs on Wednesday and word was the chief executive would come out fighting. The question of what changed Mr Diamond's view about remaining in his job is the big unknown. Between Monday evening and late that night, his attitude to staying in the job had gone from defiant to beaten. A call took place with George Osborne, the chancellor, late on Monday, though it is unclear what was said. Some people close to Mr Diamond suggest he may have been told explicitly by a senior government figure that remaining in his job was impossible. The other evolving dynamic has been a shift of opinion among shareholders about whether Mr Diamond should go. Although Mr Agius told friends earlier in the day that there was "overwhelming shareholder support" for Mr Diamond, some top 10 investors made clear that their view had changed. Over the weekend most investors had stopped short of explicitly calling for Mr Diamond's head, conscious of the instability that would result from losing the bank's chairman and chief executive at the same time. But there was a growing recognition throughout the day on Monday that Mr Agius's departure would not go far enough. A deep transformation of the bank's culture was required and, as the person responsible for building up Barclays" investment bank - where the Libor abuses took place - Mr Diamond did not fit the bill. His position will not be easily filled, however. Antony Jenkins, head of Barclays" retail arm and former head of its Barclaycard business, is considered by many in the industry as the likeliest - possibly the only - internal candidate. Mr Jenkins knows Barclays well but is not tainted by the wrongdoing that occurred in its investment banking arm. However, people who know him well have questioned his credentials as group chief executive given that the investment banking arm still accounts for more than half of Barclays" profits. Also Mr Jenkins was at the head of the retail business during the mis-selling scandal of payment protection insurance - which has cost Barclays more than £1bn - and some bankers have questioned his technical ability to lead the entire bank. External candidates include Bill Winters, JPMorgan's former head of investment banking; Hugo Baenziger, former chief risk officer at Deutsche Bank; Colm Kelleher, a senior executive at Morgan Stanley; and Richard Meddings, finance director of UK bank Standard Chartered. Bankers believe Bill Winters would be the best qualified. While, like Mr Diamond, he is an investment banker, he is highly respected and was also one of the five-member panel of the Independent Commission on Banking, led by Sir John Vickers, which set out tough reforms for the British banking industry last year.