The Northern Ireland Secretary has issued a stinging rebuke to the DUP leader, the Rev Ian Paisley, and his son, Ian jnr, over the disclosure of a purported letter implying that the Northern Secretary was suppressing information on the murder of Mr Edmund McCoy.
A spokesman for the North's First Minister, Mr David Trimble, said earlier the letter appeared to be a "malicious forgery". And yesterday Mr Mandelson stepped up the attack by telling Dr Paisley that his Assembly member son's release of the "hoax" letter brought politics and the DUP to a "new low".
The letter, supposedly written by a civil servant on behalf of the Northern Secretary, has Mr Mandelson telling Mr Trimble that it would be "damaging" to the new devolved administration to disclose who he believed was responsible for Mr McCoy's murder two weeks ago. The IRA is being blamed for the murder.
In a letter to Dr Paisley yesterday Mr Mandelson wrote: "Anyone who spends five seconds reading that letter would know it is a hoax. It is addressed incorrectly and it is ungrammatical. Even if someone was still in doubt a two-minute phone call to my office or that of David Trimble would have revealed the truth.
"That is what a serious politician would have done. Instead your son went live on air with a hoax, when he must have known that is what it was. This brings politics and, I am afraid, your party to a new low."
Mr Paisley jnr continued to insist the letter was genuine. He accused Mr Mandelson of engaging in the "politics of spin" by issuing "contemptible jibes" against the DUP. "He is the political coward, too afraid to face up to the killers of the IRA. The truth has found the Secretary of State out and he finds it difficult to cope, only offering silly jibes, not real answers to real questions," he added.
The DUP is planning to gain maximum publicity from the letter, whether or not it is authentic. Dr Paisley is today due to weigh in with further criticism of Mr Mandelson based on it. On Tuesday the RUC Chief Constable, Sir Ronnie Flanagan, said that "intelligence indications" were that the IRA murdered Mr McCoy although he could not be definite as to who was responsible at this stage.
Meanwhile, the DUP continued its attack on Mr Trimble and pro-agreement unionists by asking how the UUP could accept Sinn Fein Ministers in the Executive following the convictions of three Irishmen on gun-running charges in Florida.
"How can Sinn Fein be allowed by David Trimble to remain in the government of Northern Ireland in the light of such a development and on the day when the Chief Constable is saying that the intelligence points to IRA involvement in the murder of Ed McCoy?" said the DUP Minister for Social Development, Mr Nigel Dodds.
The Sinn Fein MLA Mr Alex Maskey said while he was reluctant to comment on the Florida convictions when that judicial process was not completed - sentencing will not take place until August - it was clear that the IRA ceasefire was intact.
"It is also clear that rejectionists are using this, and any other issues, to undermine the entire process. Their sole agenda is to destroy this process. Our agenda is to see it succeed," he said.