In furious Commons question time exchanges, Tory leader David Cameron accused Mr Brown of failing in his "duty of care" to the armed forces.
He said the Government had fought two wars "on a peacetime budget" and the Treasury had "massively underestimated" the cost of the conflict in Afghanistan.
But Mr Brown hit back, saying defence spending had risen and £9 billion had been poured into the operation in Afghanistan, on top of the general defence budget.
As the row escalated, he repeatedly taunted Mr Cameron over the "non-dom" tax status of Lord Ashcroft, insisting, at one point, that he would take no lectures on integrity from an Opposition leader who would not answer questions on the Tory deputy chairman.
It came after an inquest into the deaths of Corporal Sarah Bryant, 26, the first female casualty in Afghanistan, and three special forces comrades heard a string of criticisms over their equipment and training.
Wiltshire and Swindon coroner David Masters pledged to raise his concerns with the Ministry of Defence at the end of yesterday's inquest.
He recorded unlawful killing verdicts for Cpl Bryant and special forces reservists Corporal Sean Robert Reeve, 28, Lance Corporal Richard Larkin, 39, and Private Paul Stout, 31, who died when their Snatch Land Rover hit a roadside bomb in June 2008.
Mr Cameron repeatedly pointed to criticisms levelled at the Government by former chiefs of the defence staff over alleged equipment shortages in Iraq and Afghanistan.
As some Labour backbenchers suggested this was because the critics were "Tories", Mr Cameron reacted angrily, banging his papers on the despatch box, and demanding an apology for this "disgraceful slur" on the former defence chiefs' patriotism.
"That is what this tribalist, divisive Government thinks about people who serve our country," he said.
The exchanges began with Mr Cameron pointing to yesterday's inquest into the deaths of four soldiers in Afghanistan in 2008.
"At the time, the Defence Minister (Quentin Davies) linked their deaths to the commander's choice of vehicle.
"This was flatly contradicted by what the coroner said. So will you now apologise on behalf of your minister?"
Mr Brown replied: "The minister apologised at the time and I repeat that apology."
Mr Brown said he had read the report from the inquest and it would go to the Ministry of Defence.
"They've said they will look at every detail that is raised by the coroner and take whatever action is necessary."
Three areas had to be looked at.
"The first is on vehicles themselves, where we have ordered 1,800 new vehicles since 2006 at a cost of £1.7 billion to make sure we have the vehicles necessary for the commanders on the ground.
"Secondly, on training, we have made sure the training is better and it will be improved for those who are going to Afghanistan.
"Third, on IEDs themselves. As everybody knows the guerilla warfare in Iraq and Afghanistan led to them starting to use IEDs and we had to take extra measures to deal with that.
"We have improved our engineering capability, our surveillance capability. We have now 3,000 mine detector machines on the ground for our troops. That will double over the next few months.
"We are doing everything we can to deal with the IED threat. So we are answering legitimate questions that have been raised."
Mr Cameron said: "You've now apologised for something that should never have been said by the minister and the House will be grateful for that."
Turning to the Prime Minister's evidence to the Chilcot inquiry last week, he said: "Following your evidence one former chief of the defence staff said you were being 'disingenuous', another said you were 'dissembling'. Both these people worked with you."
It was at this point that Mr Cameron turned on Labour backbenchers, saying: "Oh, it's because they're (the former chiefs of the defence staff) 'Tories' is it? That is what this tribalist, divisive Government thinks about people who serve our country."
He told the Prime Minister: "You should get up and disassociate yourself completely from what your colleagues have said."
Mr Brown said: "It's common cause within this House that we support the campaign in Iraq and Afghanistan. It's common cause also that we do not send our troops into battle without the commanders assuring us that they are properly equipped for the operations they are undertaking.
"In every instance where the MoD asked for equipment under urgent operational requirements, that equipment was given.
"Let's find where the common ground is, rather than where there is division."
Mr Cameron angrily rose again, saying: "Your MPs have questioned the integrity of people who served this country, fought for this country, who are essays in bravery...
"And before we go on, you've got to get to that despatch box and disassociate yourself from those disgraceful remarks."
Mr Brown told him: "I've never at any time criticised the patriotism of anyone involved in the defence establishment of this country.
"But I think we should have a debate about this which is serious and based on facts.
"Every request that was made to us by the MoD for urgent operational requirements was met.
"We've spent £18 billion in Afghanistan and Iraq on top of the MoD budget.
"I assure this House that every time our commanders go into action, I ask them for an assurance that they have the equipment they need for the operation.
"I want to applaud the patriotism of everyone who serves our country and so does the vast majority of this House."
Mr Cameron said the Prime Minister had given a lecture earlier on character. "But you haven't got the character to stand up to your own backbenchers. It is a disgraceful slur.
"It's not just chiefs of the defence staff who said this. We've had a former permanent secretary at the MoD talking about a 'guillotined' budget.
"We've had a serving Permanent Secretary talking about a serious dispute between the Treasury and the MoD.
"We've had the former commander of the Paras in Afghanistan saying he was 'staggered by the lack of any sense of responsibility' from you."
He demanded: "Why do you think that all these people, dedicated to the defence of this country, are wrong, while only you are right?"
Mr Brown said he had put the facts before the inquiry on Friday. Defence spending had been rising in real terms under the Government.
"I said, in addition to that expenditure, £8 billion had been spent in Iraq and we are spending £9 billion in Afghanistan.
"The Chief of the Defence Staff has said on record that we have the best-equipped force that we have ever been.
"I'm going to take no lectures on integrity from the man who won't even answer one question about Lord Ashcroft."
Mr Cameron said that, of course, ministers had not rejected requests for urgent operational requirements. "But they never thought what that meant for the defence budget.
"The fact is you've tried to fight two wars on a peacetime budget. When you were Chancellor, the Treasury massively under-estimated the cost of the war in Afghanistan."
Mr Brown denied this, insisting the defence budget had been "rising every year" and the only time it had been cut was when the Tories were last in power.
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