In March 2003, Prime Minister John Howard announced combat operations had begun and Australian troops had crossed the border as the Shock and Awe bombardment lit up Baghdad.

The decision had been made - the invasion was already underway as Howard spoke into the TV cameras, informing Australians that we were at war.

In a democratic nation with a bicameral parliament constituted to decide on matters of state, this call was left up to Howard and his Cabinet. Seventeen people.

As Prime Minister John Howard said on that same night, "We are determined to join other countries to deprive Iraq of its weapons of mass destruction, its chemical and biological weapons, which even in minute quantities are capable of causing death and destruction on a mammoth scale."

Those claims were utterly false, and the PM already had that advice in his pocket. Since then 4693 Coalition service personnel have lost their lives in Iraq, including two Australians. At least 110,000 Iraqi civilians are estimated to have met violent deaths. Iraq now has nearly five million orphaned children.

Hundreds of thousands of Australians across Australia marched against the invasion, and I was one of them. The Prime Minister ignored us and went to war regardless.

While citizens do delegate responsibilities to leaders by electing them, the democratic system includes an ongoing forum for discussion where leaders must provide reasoning and minimal accountability for their decisions: the Parliament.

Howard's was the first government in modern history to go to war without the support of both houses of parliament. This must never happen again. The responsibility of sending Australian men and women into harms way should not happen behind closed doors - it is a call that should be made in the open by elected members and the public they are meant to represent.

That's why I've taken carriage of a Private Senator's Bill designed to amend the Defence Act (1903) to require parliamentary approval to send Australian troops to war.

A decades-old piece of unfinished business, introduced by the Australian Democrats in the 1980s, it has since been taken up by the Australian Greens as a way of giving the people a say in whether we wage war.

A debate is under way in the UK, the very source of our own Westminster system, to transfer the prerogative power to declare war, ratify treaties and appoint judges from the executive to the parliament. Our ally the United States has a similar provision that subjects the decision to go to war to a broader forum - Section 8 of the US Constitution says, "Congress shall have the power to declare War".

This bill would bring Australia into line with other democracies like Denmark, Finland, Germany, Ireland, Slovakia, South Korea, Spain, Sweden, Switzerland and Turkey where troop deployment is set down in constitutional or legislative provisions. Some form of parliamentary approval or consultation is also routinely undertaken in Austria, the Czech Republic, Italy, Japan, Luxembourg, the Netherlands and Norway.

Arguments against using our democratic structures on the grave issue of troop deployment include that it would be "impractical", "restrictive" and "inefficient". Such arguments ignore the fact that parliaments make complex and nuanced decisions, rapidly when necessary, and that the bill has been carefully drafted for circumstances when recourse to Parliament might not be possible.

While autocracies or dictatorships may well be more speedy and efficient, they are not legitimate or acceptable forms of government.

The Rudd Government has quietly aligned itself with the Opposition in pre-emptively opposing the bill. The same empty bipartisan consensus saw the Senate Standing Committee on Foreign Affairs, Defence and Trade decide against holding a public hearing into the bill, a standard part of Senate Inquiries into issues of public importance.

So on Friday 12 February I took the unusual step of convening a hearing in Parliament House, with or without the major parties. The evidence we took from an impressive witness line-up will be submitted to the committee in the form of a minority report, and placed in the public domain to further the debate.

People like Brigadier Adrian D'Hage, who is one of our most distinguished former soldiers, Professor Colin Warbrick, who assisted the UK parliamentary committee inquiry, Dr Sue Wareham from the Medical Association for Prevention of War, Neil James of the Australian Defence Association, Paul Barratt, a former Defence Secretary, and Professor Helen Ware, an author, academic and former Australian High Commissioner converged on the capital to debate the pros and cons.

I should emphasise I didn't expect all these witnesses to support the proposal (it wouldn't have made for a very interesting hearing if they did) - but each of them expressed a willingness to explore the issues and brought their expertise to bear.

We need to learn lessons from the monumental and bloody mistakes of the recent past. History, in this instance, must not be allowed to repeat.

Senator Scott Ludlam