The government was accused last night of denying British soldiers vital equipment that could have saved their lives in Iraq as a bitter party political row threatened to engulf the Chilcot inquiry into the war.

Two days before Geoff Hoon, the former defence secretary, prepares to give evidence to the inquiry, the Conservatives are demanding that it establish the truth behind claims that Hoon delayed ordering enhanced body armour shortly before the invasion because ministers did not want to alert the public to their preparations and stoke opposition to war.

The former chief of defence staff, Lord Boyce, has already told the Iraq inquiry that he had been blocked from ordering equipment and mobilising troops for several months. This meant he was left with "some very short timelines" in which to prepare troops for the invasion. "I was not allowed to speak to the chief of defence logistics," Boyce told the inquiry. "I was prevented from doing that by the secretary of state for defence because of the concern of it becoming public knowledge that we were planning for a military contribution."

In a clear sign that unresolved arguments over Iraq could spill over into the general election campaign, Liam Fox, the shadow defence secretary, told the Observer that Sir John Chilcot's investigation had to establish the truth of such claims, and of tragic cases such as the death of Sergeant Steven Roberts, the first British soldier to die in the operation to oust Saddam Hussein.

Fox said the public needed to hear an explanation from Hoon, and would expect the facts to be set out by the inquiry.

"Sgt Steven Roberts died because he didn't have the appropriate body armour," Fox said. "Geoff Hoon delayed the order for body armour from 13 September 2002 to 13 November 2002. As a consequence, body armour did not arrive into Iraq until 31 March the following year. Many believe this delay was political in order to stop the signal being sent, not least to the Parliamentary Labour party, that the Blair government had already decided to go to war in Iraq. It is time for the British public to know the truth."

Sgt Roberts, 33, from Shipley, West Yorkshire, was accidentally shot dead on the night of 23-24 March 2003, when UK troops opened fire during a disturbance near Basra. A Ministry of Defence inquiry into his death confirmed he would have survived if he had been wearing enhanced combat body armour (ECBA).

During the inquest into his death, an MoD director, David Williams, said an urgent request for 37,000 extra sets of enhanced body armour, sent to Hoon by an MoD logistics team on 13 September 2002, was returned by the minister with the annotation "further advice required", because any approach to manufacturers would in effect have announced that the UK was preparing for war while diplomacy continued. Sgt Roberts was wearing combat body armour (CBA) at the time. He had previously been issued with ECBA, but it was withdrawn four days before his death owing to shortages.

It has been reported that Hoon, who was behind the recent failed leadership coup against Gordon Brown, may be ready to accuse the prime minister of responsibility for vetoing the purchase of vital military helicopters when he was chancellor and of blocking orders for life-saving battlefield equipment.

At the inquest into Sgt Roberts's death, Andrew Walker, Oxfordshire's assistant deputy coroner, said: "To send soldiers into a combat zone without the appropriate basic equipment is, in my view, unforgivable and inexcusable."

Hoon said last night: "I will say what I have to say to the inquiry."

On Monday the inquiry will hear from Jonathan Powell, Tony Blair's former chief of staff. Hoon's appearance on Tuesday will be followed by former foreign secretary Jack Straw on Thursday. One key piece of evidence to the inquiry will be a secret letter sent by Straw to Blair in 2002 that revealed doubts over the plans for Iraq. The MP warned the prime minister that the legal case for military action in Iraq was questionable and that removing Saddam Hussein would not guarantee a better future.

The inquiry will then hear from Blair within the next few weeks and Brown after the general election.

It comes as a poll of voters finds that almost a quarter believe Tony Blair deliberately misled MPs over the Iraq war and should face war crimes charges. A YouGov survey for the Sunday Times found that the majority think the former prime minister knew Saddam Hussein had no weapons of mass destruction while 32% accept that he "genuinely believed in the threat".

• Two more British soldiers have been killed in Afghanistan, the MoD confirmed yesterday. The soldiers, from 3rd Battalion The Rifles, died in an explosion near Sangin in Helmand province on Friday. It brings the number of British service personnel who have died since the start of operations in Afghanistan in 2001 to 249.