Journalists permitted to accompany the British military to war zones find themselves in a parallel world. Instead of flying from Heathrow or Gatwick, they head for an RAF base such as Brize Norton in Oxfordshire, where the procedures are much like those at a civilian airport, but everyone, on both sides of the check-in desk, is in military uniform.
The same applies to the flight out to Iraq or Afghanistan. The public address announcements sound pretty much like those on British Airways, but the planes - TriStars or VC-10s - are often too venerable for commercial service, and the cabin staff are clad in khaki jumpsuits.
And while Camp Bastion in southern Afghanistan and Basra Air Station in southern Iraq are recognisably a long way from Britain, they resemble nothing so much as each other: British military enclaves where, thanks to the miracles of modern logistics, everything from the plastic accommodation tents to the food is exactly the same in both places. With scarcely any indigenous people about, there are few clues as to one's location.
This is the world from which one of Britain's major news organisations, ITV News, has been banned in a furious row with the Ministry of Defence, giving rise to charges of censorship. The MoD withdrew the company's access to military "embeds" - the process by which reporters, photographers and TV crews are housed, transported and protected by British troops in conflict zones - after a series of reports on ITV News about the treatment of wounded soldiers.
In an email to ITV editors, the MoD's director of news, James Clark, called the first report "as bad a hatchet-job as I've seen in years. Cheap shots all over the place, no context, no reasonable explanation. Like the Daily Star in moving pictures."
The ministry also claimed that footage of wounded soldiers arriving at Birmingham airport could have caused their families distress, and that no permission had been sought from the soldiers, who could be identified from the pictures.
"If giving ITN detailed exposure to our people, lengthy briefing and open access results in this," Mr Clark's email went on, "then I dread to think how your editors and producers would look to exploit access to our people in theatres (of war), or our chiefs and ministers." In another internal email, which was leaked, the MoD's news chief reminded military officers seconded to media operations staff that co-operation with the TV company had been withdrawn.
There will always be conflict between inquisitive journalists and the military's "need to know" approach. But the tensions, already raised by Britain's involvement in Iraq and Afghan-istan, have been turned up several notches more by coverage of the intense fighting in Afghanistan's Helmand province in recent months. Nor has the outburst by the head of the army, General Sir Richard Dannatt, who emphasised the need for British forces to leave Iraq soon, done anything to ease frictions between the media and the military's political masters.
Sensitivities can depend on who is defence secretary at the time: last year, when John Reid held the office, I visited Basra, and was not permitted a single moment with the lower ranks unless an escorting officer was present. The reason appeared to be that some of them had previously voiced their doubts about the mission in Iraq. And to judge by John Humphrys's observations from Basra on BBC Radio 4's Today programme last week, the emphasis on personal safety during an "embed" still outdistances one's ability to judge and report what is going on by a mile.
Downing Street itself intervened in the summer to halt access to the front lines in Afghanistan, after a Sunday Times journalist found herself in a life-or-death firefight and filed a dramatic report.
Now the only way to reach places like Sangin, where some of the heaviest fighting took place, is to seek a "full embed" of three to four weeks - a heavy commitment for all but the richest media organisations - which may or may not be granted.
The military on the ground argues that the undoubted shortage of helicopters makes it difficult to get journalists to the action. Helicopter movements are kept to a minimum in any case - because to shoot one down is a much-sought prize for the Taliban: a full battle group has to be deployed to protect any helicopter sent to the hot spots in northern Helmand.
But the MoD has discovered that in the 21st century it is impossible to blank out all coverage. The media gained news of the fighting from a torrent of emails, mobile phone videos and helmet camera footage sent by the squaddies themselves; instead of the usual process of giving journalists access and trying to steer them in a positive direction, Mr Clark and his colleagues found themselves constantly having to react to the latest revelation. Some of that pressure appears to lie behind his intemperate response to coverage by ITV News and other media organisations.
But if the military won't help, why don't we get to the danger zones ourselves? After all, when I first came to Afghanistan in 1992 I was able to move around freely, even though the country was in the midst of a bitter war and there wasn't a British soldier in sight. In those days "foreign journalist" was a magic password which worked at every checkpoint. Although the Afghan government militia opened fire on me, they could hardly be blamed since I was crossing the front line between them and the mujahedin.
After the 1991 Gulf war, when American troops were temporarily occupying a slice of southern Iraq, we could drive there from Kuwait and turn up unannounced at any US unit. They said we could carry on up the road and talk to the Iraqi forces if we wanted to, but we decided against taking the risk.
Sadly, the same freedom of movement is no longer possible in the post-9/11 world. With al-Qa'ida seeking to turn the conflict into one between Islam and the West, it is suicidal to venture out alone in Iraq or southern Afghanistan. Earlier this month an Italian photojournalist who set off from Kandahar towards Helmand was seized. His kidnappers are threatening to behead him.
Nor does the danger to "unilateral" journalists always come from the other side, as ITV News knows all too well. An inquest recently determined that one of its most experienced correspondents, Terry Lloyd, was shot dead by American troops in the early days of the 2003 invasion of Iraq. The Pentagon is refusing to disclose the identities of the soldiers involved: among its motives, many suspect, is to reinforce the message that this is what happens when you don't embed.
The embedding system, it should not be forgotten, is derived from British handling of the media during the Falklands war. The Pentagon, still smarting from Vietnam, where many commanders believed the war for public opinion was lost through coverage by journalists able to come and go at will, enthusiastically adopted the idea of controlling their environment, and applied it during President Ronald Reagan's invasions of Grenada and Panama.
The concept has reached its full flowering since 2003. In most of Iraq and southern Afghanistan, journalists currently have no choice but to embed if they want to go anywhere near (though increasingly not actually to) the fighting. But the information age is one of constant change, and as it becomes possible to communicate freely between almost any two points on earth, the news will emerge in other ways. The embedding system could already be past its finest hour, and ITV News may find that to be excluded from it is no great loss.