The Taoiseach has called on TDs to consider how the State investigates allegations after a probe into the controversial sale of building services group Siteserv to a company controlled by businessman Denis O'Brien took seven years at an estimated cost of €30m.

Last week, the Government published a Commission of Investigation report into the 2012 business deal.

The report found the transaction was "so tainted by impropriety and wrongdoing, that the transaction was not commercially sound".

The report was highly critical of the role of key figures in Siteserv and said the sale of the company, overseen by State-owned IBRC bank, was conducted on "misleading information".

The investigation led by Judge Brian Cregan has been estimated to cost more than €30m.

However, in the Dáil the Taoiseach said the commission's costs were €12m but added third party costs had yet to be finalised.

He added that the "experience raises a question mark for us as a legislature over what we might do to make any future investigation more timely and less expensive".

He said while he shared "frustrations" about the length of time it took to complete the report, he added he still thought it had been a "worthwhile" exercise.

The report examined one of 38 transactions which involved State-owned IBRC bank writing off more than €10m.

The Commission of Investigation is now preparing a report regarding the other transactions.

The Taoiseach said upon receipt of that report the Government would make a decision regarding the future of the commission.

However, it is widely expected within Government circles that the investigation will not go any further.

This is because it took seven years to complete the first component of the inquiry into one transaction and there are 37 remaining transactions which it could investigate.