Given that the Chilcot inquiry report is said to be four times as long as War and Peace, I suspect few of us will ever read it. This documentary play by Richard Norton-Taylor and Matt Woodhead, however, dramatically distils much of the key evidence. By including testimony from army veterans, the families of dead soldiers and Iraqi refugees, the piece forfeits the forensic purity of the Tricycle’s famous tribunal plays but it amounts to a devastating account of the mendacity, delusion and incompetence surrounding the invasion of Iraq in 2003.

Some of the external reportage leaves you pretty shaken. Testament to the insufficiency of equipment supplied to our troops is provided by the mother and father of soldiers killed in action: the former, who went on to found Military Families Against the War, explains that her son died because protective armour was never fitted to his Land Rover, while the latter reveals that a metal plate was stuck on the wrong headlight of his son’s vehicle. Two disillusioned army veterans explain how suspected insurgents were transferred to American detention centres and held in dog kennels out in the sun. A high-placed civil servant, recalling the dossier about Iraq’s supposed weapons of mass destruction, describes it as “an unutterable pile of dribble”.

The picture that emerges is of a war with unstoppable momentum

Powerful as all this is, it pales beside the evidence given to the Chilcot inquiry which confirms that the Iraq war was prosecuted on the shakiest grounds and with little regard to the consequences. We hear from the attorney general, Lord Goldsmith, whose doubts about the legality of the war were quelled after a visit to Washington; from Jack Straw who claims that the legal advice was contradictory, expresses his hesitations about military intervention but who ends by saying: “I do believe that the action we took was justified”; and from Geoff Hoon, the defence secretary, who concedes that no one in cabinet was responsible for examining the war’s aftermath.

Raad Rawi plays both Sir John Chilcot and Tony Blair in the verbatim play. Photograph: Joe Twigg

The picture that emerges is of a war that achieved an unstoppable momentum. Tony Blair cuts a particularly sorry figure in his use of 1930s appeasement and the attacks of 9/11 as a justification for war, and in his reluctant admission that we allowed a post-conflict power-vacuum to develop. After such a litany of ducking and diving, it is almost a relief to hear Eliza Manningham-Buller, the former head of MI5, unequivocally express her belief that a war in Iraq would aggravate the threat to the United Kingdom.

Woodhead directs the piece well. Thomas Wheatley, a veteran of the Tricycle inquiries, puts questions to the various authorities with lethal clarity, Raad Rawi effectively represents, at different times, both Sir John Chilcot and Blair, and Sanchia McCormack and Jonathan Coote play the bereaved parents with a controlled anger. The piece doesn’t come to any conclusions. But it doesn’t need to since the evidence speaks for itself. The play also prepares us for the publication of the Chilcot inquiry on 6 July by reminding us of the dishonesty and ill-preparedness surrounding the momentous decision to go to war.