Social Democrats joint leader Catherine Murphy is to give oral evidence before the Cregan commission, which is investigating the sale of Siteserv to businessman Denis O’Brien.

The commission is understood to have written to the Kildare North TD in recent days asking her if she would appear. A series of allegations about the sale made by Ms Murphy in the Dáil led to the establishment of the commission in 2015.

A spokeswoman for Ms Murphy said she has confirmed she will attend on a date yet to be determined.

Ms Murphy had submitted a dossier of documents to the investigation but had not been asked to give evidence in person.

Her appearance at the commission will represent a significant opportunity to investigate the claims she has made in relation to the sale of Siteserv as the Cregan commission enters a crucial phase.

The commission was established by then taoiseach Enda Kenny in 2015 to investigate all disposals, by IBRC – the former Anglo Irish Bank – that resulted in a capital loss to the State-owned bank of more than €10 million.

Mr O’Brien purchased Siteserv through his company, Millington, for €45 million in 2012. IBRC had previously given the company a loan write-down of €110 million.

Taoiseach Leo Varadkar recently told the Dáil the final price tag for the commission is now expected to top €30 million, a figure described as “extraordinary” by Fianna Fáil leader Micheál Martin.