THE DUP has said it supports the need for an independent investigation into the Renewable Heat Incentive (RHI).
The party released a statement on Sunday night in which it said it backed a probe that was "free from partisan political interference".
It meant the Ulster Unionists were alone among Stormont's main parties in the belief that the assembly's Public Accounts Committee (PAC) is best equipped to scrutinise the scheme's failings.
Critics believe the Stormont spending watchdog lacks the necessary clout to comprehensively probe the RHI scandal.
Last week, the PAC agreed to disregard convention by calling First Minister Arlene Foster to give evidence.
It has also called a number of DUP special advisers, alongside former enterprise, trade and investment committee chairman Patsy McGlone.
Sinn Féin will today call for an "independent, time-framed, robust and transparent investigation" undertaken by an "independent judicial figure from outside this jurisdiction".
The SDLP and Alliance also believe any probe should be judge-led, while the Ulster Unionists argue that the PAC, which is chaired by UUP MLA Robin Swann, be allowed to complete its inquiry.
A former vice-chairman of the committee last night said only an independent inquiry will get to the facts at the heart of the RHI debacle.
Former SDLP MLA John Dallat said the PAC's function was solely to examine reports published by the Audit Office.
"It is difficult to see how it can conduct the type of in-depth inquiry that is needed to get to the bottom of a very complex case where there are all types of allegations about who benefitted, who was to blame and even who had the worst temper," he said.
Mr Dallat said the committee's workload meant it would not wish to get "bogged down in one single report for months on end" and also highlighted the difficulties in reaching a consensus among the 11 members.
"Much of the work will be conducted behind closed doors and there is always the risk of political interference," he said.
"This is a public scandal and should be examined under the eye of the public who will pick up the bills for the next 20 years."
The DUP statement said the party supported the "need for an independent investigation, free from partisan political interference, to establish the facts around the RHI scheme".
"We are of the view that the conclusions of any investigation must be made public and that any investigation must be conducted speedily to assist in the process of building public confidence," it said.
"We have been working to reach agreement with officials and others on the precise details of such an investigation over the last number of days."
An Ulster Unionist spokesman said: "The PAC have made good progress in uncovering the facts relating to the RHI and they have a number of important sessions coming up so it is vital, as a matter of urgency, they are given full access to all documents and potential witnesses so they are able to complete their work.
"If the evidence shows there is the need for a more far-reaching inquiry, which is outside the remit of PAC, then we would give our support to that."
