Mr Finucane was shot dead by UDA/UFF gunmen at his north Belfast home in 1989. Allegations of collusion between security forces and loyalists surrounded the murder of the 38-year-old.
His widow, Geraldine Finucane, who was injured in the attack, has campaigned for an independent inquiry for more than two decades.
On Wednesday, she told a London press conference: "This report is not the truth".
The 500-page report, headed up by Sir Desmond de Silva QC, was ordered by Prime Minister David Cameron in October last year.
It found no overarching state conspiracy in the murder of Mr Finucane, but uncovered "shocking" levels of state collusion.
Reacting, Mrs Finucane said that the British Government had suppressed the truth and attempted to throw all blame on dead individuals and disbanded organisations while exonerating ministers, serving officers and existing security agencies.
She said: "Yet another British Government has engineered a suppression of the truth behind the murder of my husband, Pat Finucane.
"At every turn, dead witnesses have been blamed and defunct agencies found wanting. Serving personnel and active state departments appear to have been excused.
"The dirt has been swept under the carpet without any serious attempt to lift the lid on what really happened to Pat and so many others.
"This report is a sham, this report is a whitewash, this report is a confidence trick dressed up as independent scrutiny and given invisible clothes of reliability. But most of all, most hurtful and insulting of all, this report is not the truth."
At every turn it is clear that this report has done exactly what was required - to give the benefit of the doubt to the state, its Cabinet and ministers, to the Army, to the intelligence services and to itself.
Mrs Finucane said her family had been "misled and humiliated in a cruel and unnecessary fashion" when they were invited to Downing Street last year, only to be told that there would be no public inquiry and that instead Mr Cameron was ordering a behind-closed-doors review of documents.
"I left Downing Street that day so angry I could hardly speak," she said.
She insisted that the family came to London on Wednesday prepared to judge the report with "an open mind" and with "a faint hope" that their misgivings would be proved wrong.
But she added: "I regret to say that once again we have been proved right."
Mrs Finucane said the review had been "compiled by a lawyer with strong links to the Conservative Party who was appointed by the Conservative Government without consultation".
And she added: "The report is the result of a process into which we have had no input - we have seen no documents, nor heard any witnesses.
"In short, we have had no chance to assess the evidence for ourselves at first hand. We are expected to take the word of the man appointed by the British Government."
Mrs Finucane said she accepted the renewed apology given by David Cameron in the House of Commons on Wednesday, but suggested he had little choice but to offer one.
"I will give him the benefit of the doubt and accept the apology but it doesn't go far enough because I don't really know what he is apologising for."
The report "doesn't tell me much more" than previous inquiries, she said.
The current government has said they don't want to have a public inquiry, but the opposition have made it quite clear that their policy is that a public inquiry will be established.
Mrs Finucane said the Irish Prime Minister Enda Kenny has always been very supportive of the family's fight and said she would not be surprised if the government in Dublin now upped the ante.
Michael Finucane, Pat Finucane's son, said it wasn't possible to accept the conclusions of the report.
"We have not been involved in the process that led to the reaching of this conclusion and there has been no public scrutiny. The PM made much of this process, much of this report, he tried to highlight the positives in the report, saying that it was the most expansive analysis of the case and most extensive uncovery of the truth to date.
"He said that he opened every door in Whitehall, but what he moves across and covers over very quickly, is the fact that he didn't let anybody else look inside those doors."
He said the family will spend the next few weeks to consider the report's contents carefully and will be seeking meetings with the government in the New Year.
"I believe Ed Milliband will keep his word," he said of the leader of the opposition.
"There's been a lot of interest expressed around the world, including in the EU and in particularly in the United States about the contents of this report and whether it takes the issue forward- we don't believe it does."