A report into the loyalist murder of Belfast solicitor Pat Finucane is to be published.
The Prime Minister ordered the review, which runs to 500 pages, following security force collusion in the lawyer's death. David Cameron is to make a statement to the House of Commons on Wednesday afternoon.
Mr Finucane, 38, was shot at his north Belfast home by loyalist paramilitaries from the Ulster Defence Association in 1989. His wife was also wounded and the couple's three children witnessed the attack. The killing was one of the most controversial of the 30 years of violence in Northern Ireland because of allegations of security force collaboration with loyalists.
Mr Cameron has already accepted that collusion took place and apologised. He ordered a review by Sir Desmond de Silva QC. Mr Finucane's widow Geraldine has vowed to keep up a campaign for a full public inquiry into the gun attack, regardless of the findings of the review.
The family of Mr Finucane arrived at Westminster to read the report shortly after 8am. They have been critical of the £1.5 million probe, saying it falls short of the full public inquiry they demanded. Sir Desmond has already said his report will reveal previously highly-classified documents relating to the murder.
Mr Finucane's son John described the de Silva review as "the embodiment of a broken promise of the British Government".
He told BBC Radio 4's Today programme: "Every time the Government have said they will look into the circumstances of the murder of my father, they have done so in a way which has excluded any involvement of my family.
"Whether that be a police investigation by Sir John Stevens, whether it is a behind-closed-doors non-statutory review by Desmond de Silva, it prohibits the public - and importantly my family - from having any input, from being able to ask any questions, from being able to see any documents or hear any evidence. You don't apologise for something but then not fully admit what it is you are apologising for, and I think that's what the Prime Minister has done.
He added: "Unfortunately, the past record does not fill us with hope, but by all means we will be reading this report with an open mind. If it puts all our questions to bed then there will be nobody happier than me to move on with our lives. But this is something which doesn't just affect my family, it affects a very large section of society in Ireland. This is something that affected all sides of the community."
Pat Finucane's wife Geraldine told the BBC she did not have high hopes for the de Silva report: "I don't really expect it to tell me very much, because I will not know who he has spoken to, I will not know what he has seen, because there's too much to hide."