The cost of funding public tribunals and commissions of inquiry into wrongdoing by state agencies and individuals will reach close to €500m by the end of this year.

The State will face a bill of at least €10m to fund the investigation into the 2012 sale of Siteserv by the IBRC to a company owned by billionaire businessman Denis O’Brien.

Taoiseach Enda Kenny has been criticised by Social Democrats TD Catherine Murphy for breaking his promise to bring emergency legislation in to rescue the Cregan inquiry into certain transactions at IBRC.