The Houses of the Oireachtas Commission has said it is not possible to estimate how much money would be saved by the abolition of the Seanad.

In a letter to the Referendum Commission, the Oireachtas body’s finance officer Gina Long said the “direct costs” of running the upper house in 2012, such as salaries, expenses and members’ staff costs, were €8.8 million.

Ms Long said “indirect apportioned pay and non-pay costs” of supporting sections amounted to €9.3 million annually. There was an annual cost of “approximately €2 million” in Seanad-related pensions, she added.

The combined total amounts to €20.1 million, which is in line with the figure of €20 million that Fine Gael has been citing as part of its campaign for a Yes vote in the October 4th referendum on abolishing the Seanad.

However, Ms Long said that “it is not possible to estimate the amount of actual net savings that would accrue if Seanad Éireann was abolished”.

Campaigners on the No side have contested the validity of the €20 million figure throughout the referendum campaign.

Fianna Fáil’s campaign director Niall Collins last night described the information contained in the letter as a “major development in the referendum campaign”. He said it showed Fine Gael’s savings claims to be “bogus”.

“The idea that these indirect costs, such as heating and lighting the same building that contains the Dáil, would be saved is idiotic and has now been exposed as such,” Mr Collins said.

“Fine Gael should remove these posters immediately and apologise for insulting the intelligence of voters.”

Minister for Enterprise Richard Bruton, the director of Fine Gael’s referendum campaign, said the correspondence confirmed that “it costs €20 million of taxpayers’ money to run the Seanad every year, contrary to what the No side claims”.

“Those on the No side seem determined to dismiss €20 million as if it is not important and as if is not a lot of money.

“But the reality is €20 million is enough to pay for 350 primary school teachers, or 1,000 new Garda cars,” he said.

The Referendum Commission had written to Ms Long seeking clarification of the cost of running the Seanad following a number of requests for details.