SINN Féin last disputed claims by former DUP leader Peter Robinson that Tony Blair duped republicans over the inclusion of an Irish language act in the St Andrews Agreement.
Mr Robinson, who retired from frontline politics 18 months ago, claimed the former Labour leader and his team of "conning" Gerry Adams and Martin McGuinness.
The former first minister made the controversial claim as the DUP and Sinn Féin continued to wrangle over protections for the Irish language.
Sinn Féin is seeking a standalone Irish language act as part of the deal being negotiated at Stormont, while unionists are proposing broader cultural legislation that would include measures on Ulster Scots.
In a newspaper article published yesterday, the former DUP leader repeated the claim made by party colleague Edwin Poots last year that his party never agreed to an Irish language act as part of the St Andrews accord.
The 2006 agreement paved the way for a power-sharing government led by the DUP and Sinn Féin.
Mr Robinson accused the British government of deliberately misleading republicans and also of changing a document without the DUP's knowledge.
He said Ian Paisley was so incensed by the Blair government's deception that he vowed to conduct all future negotiations directly with Sinn Féin.
"It was Ian's assessment - and in my view an accurate one – that if the government was prepared to con Sinn Féin in the way it did they would be prepared to do the same to us," he wrote.
The former East Belfast MP said he and Martin McGuinness later spoke about the "misleading messages" they were given by the Blair government when it was acting as intermediary in negotiations.
He claimed there was only "a tongue-in-cheek" promise of an Irish language act from the British and that the issue had not been discussed in the St Andrews negotiations. He claims a reference to the act was inserted into the agreement at the talks' conclusion.
"We were told the section had been carefully and deliberately worded. It was not an issue that should cause us any concern," Mr Robinson said.
"They (Tony Blair's team) informed us that as devolution would be up and running the government would not make good its commitment as the power would be devolved."
The former DUP leader said the British government asked the parties to accept the St Andrews Agreement only "as a basis for progress" and asked them not to alarmed by the Irish language reference because "the only thing that ultimately would matter" would be the legislation to enact the agreement's terms.
"At no stage did Ian commit the party to accepting an Irish language act, and indeed we made sure there was no commitment to it in the legislation," he said.
"Instead, the government agreed to dilute any reference to the Irish language to a requirement for an Irish language strategy. They also inserted an equal requirement for an Ulster-Scots language and culture strategy."
Mr Robinson said Ian Paisley had been "intensely displeased" by the Blair administration's duplicity.
"Not only had the government changed the document without informing us, but (Ian) was unhappy about the government's deception of Sinn Fein and was concerned that, when Sinn Fein realised they had been conned, problems would arise," he wrote in the Belfast Telegraph.
"I remember him saying to me at the time: 'It's not the way to do business' – how right he was."
But former Sinn Féin culture minister Carál Ní Chuílín said the British and Irish governments, along with all the parties at St Andrews, agreed to the inclusion of an Irish language act.
"Sinn Féin wants to see that agreement implemented," she said last night.
"Peter Robinson spent nine years as first minister blocking and Irish language act, an Irish language strategy and an Ulster Scots strategy."