Like drowning in your own blood and sweat. Like mustard gas.

I thought of Wilfred Owen’s poem ('Gas! Gas! Quick, boys! — An ecstasy of fumbling. Fitting the clumsy helmets just in time'), as Corporal M pulled the pin on a smoke bomb and got the shivering crowd of onlookers to enthusiastically shout: “Gas! Gas! Gas!” at their son or wife or friend taking part in the CBRN demonstration we were watching.

Except the demonstration was heartbreakingly slow. I stood and watched my son and his new Territorial Army buddies go through the step-by-step routine of putting on gas masks, closing their skin to a chemical attack then painstakingly cleaning off any potentially deadly substance.

I counted sixteen steps and four long minutes until they were dusted white with Fullers Earth, their humanity safely protected by rubber and drawstrings and grey powder.

And all the while, the Corporal told us about Iraq and how the insurgents test out new strategies on the Americans first and, if it’s effective (“which, let's face it, it usually is”), try it out on the Brits in the South: “And if we don’t stop them in Basra, they ship it across to Afghanistan and use it on our lads there.”

We all wanted to believe him when he told us that so far the Brit's Basra shield was solid. But suddenly this day out to watch our loved ones play at being soldiers had got serious. Suddenly this was my son slowly suiting up against faster, deadlier enemies he may actually have to face.

But this chlorine thing – where do they get barrel loads of 100% chlorine from in Iraq? “Water treatment plants? Who knows”.

Ex-Halliburton maybe, part of the millions of dollars worth of US goods gone missing in Iraq’s fraud free-for-all? Or back-street factories distilling the chemical from household bleach? Or left-over stores from the salad days of Saddam and private swimming pools and full hotels? Who knows indeed?

And how many of these chlorine bomb attacks have there been? “Fifty-eight so far”, according to the Corporal - and he’s the one with an interest in keeping count. (Chlorine attacks in Iraq spur warnings in US)

However, nasty though it sounded. It’s not the chlorine bombs that are killing British soldiers out in Iraq. And it’s not the chlorine bombs worrying the generals. It’s the increasing sophistication of militant attacks on US and UK troops.

IEDs (improvised explosive devices) buried beneath roads and hidden in cars still kill the majority of soldiers, but it’s the rise in follow-on attacks and complex ambushes that worrys the generals - the IEDs set to catch the patrolcoming in to rescue soldiers injured from a first bomb.

General Sir Richard Dannatt, in a speech picked up by the press a few months ago for comments berating the lack of town parades and flag-waving for returning British troops, spent rather more time talking about the complexity of fighting in Iraq. He said how Iraq militants were well-organised, fielding violent attacks “through the use of complex ambushes and IEDs.”

He quoted a report from an un-named commander in Iraq, describing a recent operation to illustrate that complexity:

'The op had everything: accurate indirect fire as we left the Palace causing 2 casualties; a sniper engagement onto an IED team: 4 rounds, 3 enemy dead; an AH strafing run onto militia gunmen controlled by a Forward Air Controller; a Warrior driver in his hatch killed by an enemy sniper; 3 massive IEDs with casevac and recovery under fire; and a 20-30 man JAM ambush on the extraction with small arms fire & RPGs, defeated by Warrior, Bulldog and a Javelin missile.'

“3 massive IEDs with casevac and recovery under fire.” We watched our part-time soldiers demonstrate the correct procedure for recovering wounded in a battle zone. The emphasis was on being ready for a follow-on attack while you’re sticking field packs on shattered flesh from the first bomb.

The students and electricians and nurses and office workers were demonstrating how they’d passed their CBRN (chemical, biological, radiological or nuclear) and field first aid and other tests as part of their basic army training – the series of short and intense sessions that show they are fit to serve.

The assembled families and friends who’d come to celebrate the TA troop’s Passing Out – the completion of their basic training – were told how the Territorial Army wasn’t the cosy drinking club it used to be, the British Army is stretched to breakpoint and needs everybody who signs up.

These part-time soldiers are part of our Forces and are expected to train to fight alongside the regulars, which is why hundreds of them are in Iraq right now, despite the slow reduction in British troops.

I was as proud and scared as any other mother who has seen her child march past, arm raised in a salute that’s a farewell to family.

In the Naafi afterwards, the newly-minted soldiers and the old hands were suddenly a club that the rest of us didn’t belong to. They were glad we were there, that we were “showing support” but we could never understand this club of people who had been shot at, or might soon be shot at.

In 2003, 46,000 troops were sent to Iraq at the peak of Operation Telic, 12,580 of them TA reservists - five of who died there.

The special problems facing returning TA soldiers, expected to just quietly slip back into their civilian jobs and ‘normal’ life after months spent in a war zone has led to calls for better supportfrom the armed forces, the government, NHS and employers. The criticism is that many feel isolated and unable to cope, left to struggle with psychological and physical wounds without the support network of the Forces 'family' that regular soldiers can draw on.

According to Armed Forces Minister Adam Ingram, about 300 reservists are serving in Afghanistan, and 400 in Iraq right now. The equivalent of 21 infantry battalions (around 13,000 personnel) have been deployed by the Territorial Army on operations over the last three years.

But that hasn’t stopped the government from slicing £5m off the TA budget over this year and next this year and next.

The cuts mean that “essential” new TA units promised by the government in 2005/6 will be delayed until 2009, or not happen at all. And, despite TA membership being at an all-time low of 32,000, the money for recruitment will be drastically cut. (House of Commons, Armed Forces Personnel discussion 21 June 2007)

All the men training my son and his fellow TAs to be battle-ready had served in Iraq at least once. Cpl M had been there twice, I asked him which posting had been worse? “Iraq the first time, because we didn’t know what we were doing and what to expect.”

They still don’t know what to expect, but they know what they’re doing. The Corporal tried to reassure us: “The militants aren’t ignorant tribesmen. They’re intelligent and they’re good fighters. But, like I keep telling the trainees – they’re good but the British Army is better.”

You’d better be, I thought; that’s my son you’ve got now.

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173 British soldiers have died in Iraq to date. Forty-six have died this year so far – six of them were 21, the same age as my son Here they are:

Kingsman Alex Green, 2nd Battalion The Duke of Lancaster's Regiment, from Warrington

Private Luke Daniel Simpson, 1st Battalion, The Yorkshire Regiment, from Howden, near York

Rifleman Daniel Lee Coffey, Second Battalion The Rifles, from Exeter

Private Jonathon Dany Wysoczan, First Battalion The Staffordshire Regiment, from Stoke-on-Trent

Private Kevin Thompson, Royal Logistic Corps, from Lancaster

Lance Corporal James Cartwright, Badger Squadron, 2nd Royal Tank Regiment.