War in the Gulf could be avoided if Saddam Hussein is tried before an Iraqi court or forced into exile, a Foreign Office minister has said.

The statement came as Tony Blair branded the Iraqi leader "rattled and weakened" by the growing threat of military action.

Speaking in the Commons, Mike O'Brien declined to give a commitment that Britain could seek to indict Saddam for breaches of international law.

Labour backbencher Ann Clwyd said the government had been sitting on proof of human rights abuses for two-and-a-half years.

"We have all the evidence we need to indict leading members of the regime," she said.

But the minister said criminal prosecutions would be a "matter for police and the prosecuting authorities".

He was "sympathetic" to her wishes but had to operate within the law.

"We don't accept the principle of trials in absentia in this country. It is the case that we need to continue to look at these matters," he added.

O'Brien later said ministers would be happy to see Saddam "out of Iraq and behind bars".

"We have to, however, operate within the circumstances prescribed by law and that is the way government ministers are expected to act," he added.

"However, in principle we obviously want to see someone like Saddam Hussein answer for his crimes and the best play for him to answer in practice would be before a properly constituted Iraqi court in a democratic Iraq."

Tory frontbencher Alan Duncan backed the use of international law but cautioned that decisions might not be so "black and white".

He warned of "vexed moral decisions" in the coming weeks.

And he gave his backing to Donald Rumsfeld's suggestions that exile for senior Iraqis would be a "fair trade" to avoid war.

"Unpalatable though it would be, might not exile for a few guilty men be better than death for perhaps thousands of innocent people?" Duncan asked.

The minister said that option was unlikely to emerge.

"Given a choice between peace and war I agree that we would prefer peace and Saddam exiled if he would do that, but I fear that might not be the option facing us," said O'Brien.

As MPs debated how to overthrow the Iraqi leader, the prime minister revealed that a post-Saddam Iraq was already on the agenda.

"The one thing that is very obvious is that as a result of the military build-up and as a result of the determination to see this thing through, the regime in Iraq and Saddam are weakening," Tony Blair said on Tuesday.

"They are rattled, they are weakening, we are getting a massive amount of intelligence out of there now as to what is happening in Iraq, and that is why we have to keep up the pressure every inch of the way."

But the prime minister pledged that the territorial integrity of Iraq would "sacrosanct" once he had been defeated.

"I think it is important that we try to make sure that any potential successor government has the requisite stability but also as broader representation as possible," he said. "This something we are discussing now."

But the prime minister held back from detailing the expected shape of a post conflict Iraq.

"One of the things I'm wary about at this point in time is saying 'well this exactly we should believe should happen' in circumstances where we haven't actually got to the point of saying we should have a conflict," he said.

Calls to rid the Middle East of Saddam have raised fears that state boundaries in the region could unravel.

Northern Iraq is contested by Kurds, and an independent Kurdistan would redraw Turkey's borders.

Such an outcome would be strongly opposed by Ankara, which already faces internal conflict over Kurdish independence.

In the south, "marsh" Arabs are seeking to become part of Iran - a country also drawn into the Kurdish question.

Questioned by the Commons liaison committee, Blair committed the West to preserving Iraq's borders.

"Part of any preparations is to make it clear that the territorial integrity of Iraq is sacrosanct," he said.

"There must be no changing of that whatever."

The US-led alliance is in "detailed discussions" with countries like Turkey on Iraq's post-Saddam future, Blair revealed.

"We must make sure we do everything can then to follow through. Military conflict, if it comes to that, is not end of this issue."

"There's the humanitarian questions, there's questions on what type of government... there are a whole set of issues in the north and south that need to be addressed, we believe they can be," he assured MPs.

And the British leader pledged that the West would not walk away from Iraq once any war was over.

"You can not engage in military conflict and ignore the aftermath," he said.

"So if we get to the stage of military conflict we have also got to have a very proper... plan as to what happens afterwards."