For Britain, the debate on Afghanistan is in some ways even more agonising than the debate over Iraq was. It is much more intense than the analogous debate in Australia, but the resonances between the two are uncanny.
What are the implications of Afghanistan for the British way of war? And for Britain's force structure?
Britain has a peerless naval tradition, and thinks of itself as a maritime nation, a great trading island with a need to protect vital sea lanes. But Afghanistan shows the overwhelming need for boots on the ground, for more and better-equipped infantry.
The parallel to the Australian debate - how do we decide between ships and planes for the defence of the sea/air gap to our north versus more soldiers for war among the people - is eerie. So is the alliance consideration. Britain lives in Europe, as Australia lives in Asia. But it understands that the US alliance is vital to its security and that the US position in the world is central to global security. London, like Canberra, is not going to abandon the US in Afghanistan.
In fact, the indications are strong that Britain could add an extra 1000 troops to its existing deployment of 9000 in Afghanistan. There has been speculation in the British press that Australia could also increase its modest commitment of 1500 troops. Canberra would be well advised to do this. Britain's population of 60 million people is almost three times that of Australia. Yet our troop commitment is only one-sixth of Britain's.
Australia derives immense prestige from the quality of its troops, and the government's willingness to put them in harm's way when a cause is just and urgent. In fact, these qualities have been displayed much more strongly by the British. More than 200 British soldiers have died in Afghanistan, about 20 times the Australian figure.
Yet no party with a chance of government in Britain is contemplating withdrawal from Afghanistan. The traditional third party, the Liberal Democrats, have said they'd like to wrap up the commitment soon. But even they are not quite in the cut-and-run or, in the British tradition, "butcher-and-bolt", camp.
The Labour government of Gordon Brown and the Tory opposition of David Cameron are determined to stick it out.
A final parallel between Britain and Australia is the sense that the campaign in Afghanistan is directly related to the terrorist threat they face. Most of the terror attacks and plots directed at Britain have come from Pakistani sources and have been influenced by al-Qa'ida and Taliban-linked figures operating on either side of the Afghanistan/Pakistan border.
Similarly, most terrorists who have murdered Australians have been trained in Afghanistan, or trained by Afghan alumni.
But there are obvious differences between the British and Australian debates. The British debate is vastly more intense because of the size of its commitment and the number of casualties.
Moreover, both Kevin Rudd and Barack Obama always opposed their countries' involvement in Iraq. But both supported the Afghan campaign. Both could make the switch from the bad war to the good war on attaining government.
But the British Labour government authored both the Iraq and Afghan commitments. The two wars are closely associated in the British public's mind. The British and Australians have also learnt in Iraq and Afghanistan the unpalatable truth that the best troops in the world are the Americans.
Major General Jim Molan, the only Australian general with operational experience in Iraq, went there in full possession of a potent Australian myth - that while our soldiers didn't have all the hi-tech gadgetry of the Americans, man for man they were better soldiers. He came away realising he had been mistaken.
The British had their own version of the Aussie myth. They went into Iraq telling everyone who would listen that with their experience in Northern Ireland, and Malaya before that, they knew counter-insurgency better than anyone, including the Yanks. That is a boast you no longer hear in intelligent national security circles in London.
Robin Niblett, the head of think tank Chatham House, was one of many security figures I spoke to in London this week who sombrely acknowledged this point. "There is a self-perception in the UK that we weren't as good as we said we were, and that our Basra (Iraq) stay was a bit of a blot," he said.
"We overplayed this softly-softly stuff. Perhaps, like the US at that time, we simply didn't have enough troops in Iraq. Our tactics could have worked. But our self-perception is that we didn't live up to our own PR."
But the British public also sees an element of policy failure in Afghanistan. Said Niblett: "Part of the reason for popular frustration is that we've drifted into a high-intensity insurgency in Afghanistan. We went along with the US in shifting the focus to Iraq, then found the insurgency had spiralled out of control in Afghanistan. There is a frustration that we didn't plan this right and think it through in the first place."
There is also public anger about the equipment deficiencies British troops have faced. "We're sending more helicopters, and vehicles resistant to improvised explosive devices," Niblett said. "Why wasn't that a priority in 2005-2006? There is a sense that this government is behind the curve and the troops are paying the price." Nonetheless, Niblett offers three reasons why he believes Britain will stick with Afghanistan.
"The US, under General (Stanley) McChrystal, does have a new strategy. They were focused on killing people, now they're focused on protecting people. The Americans say they have 12 to 18 months to prosecute this strategy. They will bring the lessons learned from Iraq.
"Britain cannot afford to go back to an Afghanistan ruled by the Taliban. We could live, very unhappily, with warlords or even a drugs trade, but not with a Taliban government with a footprint across the Pakistan border.
"Second, we're going to support Obama in this new strategy. We would always have thought this was the right strategy. Britain is with him for this term. The Conservatives would be the same."
Niblett's comments underline how McChrystal's new approach of switching to a classic counter-insurgency focused on protecting the civilian population, with an accompanying demand for enough troops to give the strategy a chance of success, has injected new life into the coalition effort in Afghanistan. And Niblett's third reason Britain will stay? "We've lost troops." No Government would want that loss to be in vain.
There is a view in some Western intelligence and security circles that it would be better to abandon Afghanistan. The Pakistanis could probably make their peace with the Afghan Taliban, while destroying the Pakistani Taliban, so this thinking goes. Meanwhile, the US-led coalition could leave Afghanistan alone but attack from the air the minute terrorist training camps are reconstituted or whenever Afghanistan poses any other direct threat.
Niblett rejects this view: "I don't think the idea of abandoning Afghanistan has much resonance. Look at what Afghanistan was under the Taliban.
"There is a lack of confidence that intelligence plus external targeting will get you what you need. Countries need governments that are in control of their territory, that you can deal with. The connection between the Taliban and al-Qa'ida makes it the wrong government."
But the Afghanistan campaign will cost the British government more than pound stg. 2.5billion ($4.6bn) this year. Britain devotes a substantially higher proportion of its national wealth to defence than Australia and it has been much harder hit by the global financial crisis.
This means cuts in the British defence budget during the next parliament. "This is potentially a 1945 moment for British defence," says Michael Clark, the head of the Royal United Services Institute. "The army says this is what conflict will look like over the next 30 or 40 years. Even in a China-US conflict it would be among the people somewhere.
"The navy says 'yes, we must prevail in Afghanistan' but we are fundamentally a maritime power. Look closely at the world over the next 50 years. We'll be protecting giant LNG (liquefied natural gas) tankers among other things."
Clark envisages cuts as great as 14per cent in real terms in the British defence budget over the next four years. As if to bear Clark out, Brown announced this week a cut in Britain's nuclear missile fleet from four submarines to three. It was sold as a step along the road to nuclear disarmament. but it is not without its costs.
Henry Kissinger once told me that he thought it profoundly important that Britain and France keep their independent nuclear deterrent capabilities. He thought it highly beneficial that US politicians not be the only Western leaders forced to think through and bear the responsibility for nuclear weapons.
The Americans for a long time have wanted the British to remain a great military power. Officially, Australia has long supported this, too. Judged by their commitment in Afghanistan, the British people seem to want this themselves. But sustaining it in the face of a long, bloody counter-insurgency, combined with a global economic crisis, is full of challenge.