In an earlier case involving deaths arising from the Northern Ireland Troubles, Lord Denning rejected an action by the Birmingham Six, saying that their success would mean the police were guilty of violence, threats and perjury. This, he said in court, was such an appalling vista that every sensible person would say it could not be right for the action to proceed. In the Commons today David Cameron frankly acknowledged that Sir Desmond de Silva's report on the murders of Pat Finucane and others had exposed another appalling vista.

It was not the first time that the Prime Minister had delivered a forthright and straightforward apology for something that happened in Northern Ireland: he won huge praise for doing so over Bloody Sunday. Fewer died in the Finucane episode than on that occasion, yet some may think it was even more deplorable in that it involved far more than an army unit that went out of control.

Intelligence is supposed to be about saving lives, but this report paints a picture of army, police and MI5 officers coolly and methodically making decisions about who should live and who should die. Most of the agents and informers used to infiltrate the paramilitaries were themselves actively involved in terrorism: amid the paramilitary squalor there are few moral absolutes. Yet the de Silva report lays out in 500 pages of intricate and unsparing detail a saga that Mr Cameron several times today – entirely correctly – described as shocking.

In the case of Pat Finucane, intelligence agencies were aware of several threats to his life but did not alert him to them. The last threat reached MI5 in December 1988: less than two months later he was dead, shot 14 times with a gun stolen from the army. Far more attention was paid, the report concluded, to individuals under threat of attack from the IRA. It uncovered one MI5 memo which remarked that the head of Special Branch was "unlikely to trip over himself" to safeguard republicans regarded as a thorn in the side of the security forces.

The report confirms that state agents played key roles in the murder, actively facilitating the assassination, and that the loyalist organisation involved obtained around 85 per cent of its information from sources within the security forces. In sum, the report concluded – and the Prime Minister accepted – that there was considerable doubt whether the solicitor would have been murdered without the involvement of elements of the state.

After the deed came a cover-up of startling proportions. Police and army intelligence moved heaven and earth to obstruct successive inquiries. They lied, the report concluded: they may even have started a fire that broke out in Lord Stevens' office during his investigation. Army officers and defence officials, the Prime Minister said grimly, gave the Secretary of State for Defence "highly misleading and factually inaccurate advice". Only the Cabinet of the day was exonerated, the report finding no trace of ministerial knowledge of what went on.

Mr Cameron gave every appearance of meaning it when he said he found it all "really shocking", while ruling out a full public inquiry. And on the face of it, that is right, in that Sir Desmond de Silva has probably uncovered what there is to uncover. But it is not just the continued pressure from the Finucane family that militates for a full inquiry. The depth of the depravity, the cynicism of the cover-up and the complicity of the state are all so reprehensible – and so contrary to everything this country stands for – that something more is surely required.