Two former DUP special advisers are at odds over whether a bid was made to delay cutting the cost of a botched green energy scheme in Northern Ireland.
Arlene Foster's former adviser Andrew Crawford said he never tried to postpone cost controls which civil servants wanted to introduce in October 2015 as the Renewable Heat Incentive (RHI) spiralled out of control.
Tim Cairns, who worked with former Stormont enterprise minister Jonathan Bell, disagreed.
The RHI public inquiry chairman, retired judge Sir Patrick Coghlin, said: "One of you is accurate or telling the truth about that - not both."
He said he was trying to assess their credibility, adding: "Both of those cannot be true."
Mr Cairns acknowledged their accounts differed.
Earlier stages of the inquiry have heard there was a mistaken belief among those involved in designing the RHI that the Treasury would pick up the bill for overspending on subsidies.
The intention was to have as many as possible enrolled to attract funds to Northern Ireland.
Mr Cairns said he believed the bill for RHI was being covered by Westminster and it was a "valid" step to delay change beyond the October 1 date favoured by civil servants.
He said: "It's better to be spent in Belfast than Bristol."
The scheme became over-subscribed by wood fuel burner owners and threatened to incur a massive overspend on public coffers.
Concerns centred on how long it took to close after civil servants became aware of the flaws.
The devolved powersharing institutions collapsed early last year after Sinn Fein walked out over the DUP's handling of the RHI, and repeated rounds of negotiations have failed to resurrect them.
Mr Cairns disclosed details of exchanges between party advisers around the closure of the scheme.
On 20 July 2015, he received an email from Dr Crawford, his predecessor as DUP adviser at the Enterprise Department.
Dr Crawford warned him that cuts to subsidies were expected to come in October and "you are going to get a massive spike of applications before this date".
Mr Cairns said he passed the information on to a civil servant.
Sir Patrick said Dr Crawford instructed Mr Cairns to call him to discuss the RHI scheme. Mr Cairns expressed regret that there was no written record.
"With hindsight it is abundantly clear to me that we really should have just sat round the table, got everybody interested around the table, and got this thrashed out.
"I was relying on phone calls and this shuttle diplomacy that really was deficient.
"You have to be able to say that you did your best or, electorally, that is going to be a problem."