Lorraine McCabe wrote to Mr Shatter on April 6, 2011, around six months after her husband first made a complaint to his bosses involving around 40 cases of malpractice and corruption.

She told the minister she wanted to make a complaint against Assistant Commissioner Derek Byrne, to whom her husband had presented his complaints.

She said wrongdoing had been covered up and hidden and described the “hurt, stress, annoyance, severe damage, and sheer hell on our family and family life”.

According to the report by barrister Seán Guerin, Mrs McCabe “said that they had recently received a death threat from a certain member of the force, but that she would not let her husband report it because she was afraid of the repercussions. She asked the minister for help.”

Mrs McCabe’s letter to the minister was prompted by an incident in Mayo, when a tape emerged of a garda telling a protester at the Corrib gas pipeline to “give me your name and address or I’ll rape you”.

She told the minister she was disgusted by the conduct of gardaí involved but that her husband had encountered similar but worse conduct by gardaí in Cavan.

The minister’s private secretary replied to Mrs McCabe and suggested she should make a complaint to the Garda Síochána Ombudsman Commission.

The letter also said that, given the “extreme seriousness” of the allegation of a death threat, it would be brought to the attention of the Garda Commissioner.

She wrote to the minister once again on May 5, 2011, expressing her frustration with how her earlier complaint had been handled.

The private secretary replied the following day, stating it would be brought to Mr Shatter’s attention.