Lawyers working at the Moriarty Tribunal, which has yet to publish its final report after 13 years, conducted an extraordinary lobbying campaign for a significant hike in their legal fees, including explicit warnings of imminent resignations from the tribunal team, documentation obtained by the Sunday Tribune reveals.

The correspondence between the Tribunal legal team – accompanied on occasion by supportive handwritten letters from the Tribunal's Judge Michael Moriarty – and the Department of the Taoiseach and the Office of the Attorney General dates back to the period before and after the 2002 general election and was released under the Freedom of Information Act.

The three senior lawyers at the Moriarty Tribunal – John Coughlan, Jerry Healy and Jacqueline O'Brien – have been paid a combined €23.6m (including VAT) in legal fees since 1997.

But correspondence and notes of meetings from 2001 and 2002 show they were extremely unhappy with their then daily rate of €1,200- €1,840, which they argued was far less than barristers in other less demanding inquiries were being paid. The barristers consulted with economist Colm McCarthy, later of An Bord Snip Nua fame, to buttress their claims for an increase of up to 58%.

The letters between the officials, including the country's most senior civil servant Dermot McCarthy, are at times extremely tetchy with McCarthy at one point accused of "a breach of trust".

Following meetings with the tribunal lawyers, McCarthy told then-taoiseach Bertie Ahern that "there is the prospect of some immediate departures from the team" and the government finally acceded to the demands for an increase.

The correspondence throws further light on the circumstances surrounding the government's controversial decision to follow through on its offer of a daily rate to senior counsel of €2,500, despite realising that this was an error and the rate should have been €2,250.