When six members of the Finucane family set off on their travels to London yesterday morning they could not have been expecting the news they got in Downing Street.

Pat Finucane’s three children — John, Michael and Katherine —made the journey with their mother Geraldine and uncles Seamus and Martin. The family solicitor Peter Madden was with them, and Jane Winter.

They were in London expecting to hear details of an inquiry, the inquiry they have been demanding and waiting on for more than 20 years.

The details had been a matter of speculation for about a week, and no-one had moved to dampen expectations. No-one had thought it a good idea to prepare the Finucanes for yesterday’s bad news, to get word out that it was not an inquiry, but a review that the Government had decided on.

But not long into the Downing Street meeting the shock was delivered by the PM himself. He was in the room with the Secretary of State and a number of officials.

We can only imagine the anger in Geraldine Finucane’s voice when she asked for the meeting to end after minutes. The family told the Prime Minister to his face that he had “made a mess” of the Pat Finucane affair.

After more than 20 years, all of this happened in a matter of moments.

And one wonders why Mr Cameron and his advisers thought it would be a good idea to bring them to Downing Street — bring them there to let them down.

The Government could have had no expectation that what they were offering was going to be acceptable.

Everyone knows the Finucane bottom line is a public inquiry. And anyone who has followed this case over a period of two decades and more would have known that the family would immediately dismiss the type of review that was proposed — a review the Government believes is the best and most effective way of getting to the truth.

But John Finucane is right. This is a step back from the inquiry proposed by Judge Cory, and the question is why? Who is afraid to put this case under the bright lights of public scrutiny? How ugly is the truth?

And who fears it most — the agents, handlers, the places of Army and Special Branch intelligence, those worlds of high politics, national security and official secrets?

This is a killing that enters the murkiest corners of a dirty war.

When he was Commissioner of the Metropolitan Police, Lord Stevens reported that the Finucane killing could have been prevented. His work extended beyond the specifics of this shooting, with his three inquiries putting the wider question of collusion under a spotlight.

“Collusion is evidenced in many ways,” he reported in 2003. “This ranges from the wilful failure to keep records, the absence of accountability, the withholding of intelligence and evidence, through to the extreme of agents being involved in murder.”

Had Sinn Fein said it, it would have been dismissed as lies. But the words were written by Britain’s most senior police officer at the time.

“Informants and agents were allowed to operate without effective control and to participate in terrorist crimes,” he wrote.

“Nationalists were known to be targeted, but were not properly warned or protected. Crucial information was withheld from senior investigating officers. Important evidence was neither exploited nor preserved.”

The truth of the Finucane murder would disturb the narrative of the Northern Ireland conflict, would expose the plays of a dirty war, and would ask the most awkward questions of figures in security, intelligence and politics.

Is this why there is no public inquiry? Is this why the Finucanes travelled home from London empty-handed?