THREE out of five voters thought it was a bad idea for the Government and the independent referendum watchdog to both produce information guides on the EU fiscal treaty vote this year.
A senior judge also warned the Coalition that its own private referendum information campaign caused "confusion" among voters.
The funding for the independent Referendum Commission was also halved once the Government began running its own campaign.
The advice from High Court judge Kevin Feeney places further pressure on ministers after they went ahead with their information campaign for the Children's Referendum, which cost €1.5m and was subsequently ruled unlawful by the Supreme Court.
In his report on the EU fiscal treaty referendum campaign, the then Referendum Commission chairman was highly critical of the Government's parallel campaign and repeatedly referred to the "confusion" caused.
"The distribution of two guides of similar size and appearance led to confusion among voters. This was compounded by the fact that the Government guide contained no contact details," he said.
Research by the Referendum Commission found that 58pc of voters said the distribution of two information guides at the same time was "unhelpful".