“The overall impression given by the internal Garda investigative process was that complaints or matters of concern were put through a process of filtration or distillation so that, by the end of the process, any matter of concern had been removed as a form of impurity, and only what was good was found to remain.”
Shell sparked anger last night after it announced profits of nearly £50million a day as motorists are hammered at the petrol pump.
The oil company reported profits of £4.1billion for the first three months of 2011 - up 41 per cent on the same period of last year.
The big increase, which was marginally ahead of City expectations, reflected the latest hike in oil prices and better margins in refining.
Upstream production was down 3 per cent but this compared with an 11 per cent drop at BP over the same period after the oil giant was forced to sell assets in order to pay for clean-up costs in relation to the Gulf of Mexico oil spill.
BP announced yesterday that its profits fell 2 per cent to 5.48 billion US dollars (£3.32 billion).
Shell chief executive Peter Voser has responded to the difficult conditions in downstream operations through restructuring initiatives and has refocused the Anglo-Dutch firm's efforts on emerging growth markets.
Mr Voser said: 'We continue to make good progress in implementing our strategy - improving near-term performance, delivering a new wave of production growth, and maturing the next generation of growth options for shareholders.
'The big boost to Shell's results came from a sharp turnaround in the performance of its downstream arm, which saw profits more than double to 1.65 billion US dollars (£1 billion) in the three months.
Richard Hunter, head of equities at Hargreaves Lansdown stockbrokers, said Shell's shares were up 17 per cent over the last six months, compared to a gain of 7 per cent.
He said: 'Whereas BP has had to reorganise its business model and turn its attention to the ongoing fallout from the Gulf of Mexico spill, Shell has continued to power ahead unabated.
'Particular tailwinds, of course, have come in the form of the higher oil price and improved refining margins. Even so, the company's longer term plans, including the disposal of non-core operations and additional focus on continuous improvement, give Shell a focus which should further underpin its position.
Shell added that higher UK taxes and reduced tax breaks for decommissioning rigs might cost it up to 900 million US dollars (£544 million) next year, raising fears that it could cancel some smaller projects in the North Sea.
Chancellor George Osborne recently shocked the industry by increasing the levy on profits from North Sea oil and gas production from 20 per cent to 32 per cent.
Meanwhile, industry leader Exxon reported net income of 10.65 billion US dollars (£6.4 billion) for the first three months of 2011, compared with 6.3 billion US dollars a year ago, after revenues increased 26 per cent to 114 billion US dollars (£69 billion).
The results surpassed Wall Street estimates and fuelled anger over high petrol prices in the United States. However, the company noted that less than three cents of every dollar it earns comes from the sale of gasoline and diesel fuel.