"How can it be that it takes 20 years to buy a ship, or aircraft, or tank? Why does it always seem to cost at least twice what was thought?"
"Even worse, at the end of the wait, why does it never quite seem to do what it was supposed to?"
He concluded the current programme is unaffordable in the long term and the MoD's procurement section should be privatised.
"The problems, and the sums of money involved, have almost lost their power to shock, so endemic is the issue," wrote Mr Gray.
"It seems as though military equipment acquisition is vying in a technological race with the delivery of civilian software systems for the title of 'world's most delayed technical solution'. Even British trains cannot compete."
The report warns the MoD has a "substantially overheated equipment programme, with too many types of equipment being ordered for too large a range of tasks at too high a specification".
Agile enemies such as the Taliban were "unlikely to wait for our sclerotic acquisition systems to catch up", he said.
Shadow defence secretary Liam Fox described the report as "very damning"
The Gray dossier also found delays in the shipbuilding programme meant Britain could not have fought a Falklands-style campaign any time over the past 20 years.
"We would have risked significant casualties, the very significant costs of acquiring adequate equipment at short notice (if available) or the embarrassment of not fighting at all," he said.
The report was originally commissioned by John Hutton, who resigned as defence secretary in June, and it was due to be published in July.
An MoD spokesman said Mr Gray's work will "feed into" its recently announced defence green paper and the government will publish the report in "due course".
"We are constantly improving the procurement process which has seen us deliver £10 billion of equipment to the front line over the last three years," he added.
Parts of the report had already been leaked and the BBC's political correspondent Laura Kuenssberg said its findings were expected to be critical.
But it was understood the government had decided not to go ahead with publication because the conclusions were so stark, she added.
Shadow defence secretary Liam Fox described the report as "very damning".
Mr Fox told the BBC: "It's not clear now to any of us what the size of the black hole is; and whether in fact our whole defence budget is some sort of confidence trick which tells us we are going to have equipment in the future, for which no money has been put aside.
"It's simply not good enough for the government to suppress a report of this importance.
"The conclusion the public will come to is we have a government of smear and fear at a time when we need leadership."
The leaked dossier is likely to fuel the ongoing political row over equipment levels for troops, which have particularly focussed on helicopters.
Last month, the Commons defence select committee said a lack of helicopters was undermining UK forces' operations and troop protection in Afghanistan, where the British death toll has now reached 206.
Criticism has also come from within the government's own ranks. Foreign Office minister Lord Malloch Brown had to row back from his comments after telling a newspaper, "we definitely don't have enough helicopters".
The head of the Army, General Sir Richard Dannatt, has called for better equipment to protect troops from roadside bombs in Afghanistan.
But the government has repeatedly insisted the Army has enough equipment and denied claims of a helicopter shortage.
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