It's not yet 9am on a blisteringly hot morning and ZOO is being violently ill on the side of the road.

We're in complete agony as our recently digested breakfast makes an unwelcome reappearance. Silently, we're wondering what the hell we've signed up for.

We're at an army barracks in Catterick, north Yorkshire with the prestigious P-Company (the "P" is short for "Pegasus"). P-Company prides itself on running a gruelling rite of passage for the British Army's elite band of men: those who want to secure entry into the Parachute Regiment - or the "Paras". There isn't a more physical test in the entire Armed Forces than the five-day hell that is "Test Week". Half who take on
P-Company fail and it's the only recruitment process to never be passed by a woman.

"This isn't simply about proving your fitness," Major Sam McGrath, Commanding Officer Of P-Company, tells us. "Test Week is where we separate those with Para DNA from regular soldiers. Our recruits' bodies have never endured anything like this." Gulp...

Foot-Sized Blisters
We've come to Catterick at Test Week's halfway point. After arriving late at night, we've had just a few hours kip before Sgt Ryan Swindale - soon to become our chief tormentor - is demanding our presence at P-Company HQ. It's 6am. Not a good start.

Shuffling across to the training centre, we realise we are the only ones walking. Everyone marches at Catterick.

Before suiting up in our "personalised" ZOO uniform, we drop in on the physio room. Countless recruits are being patched up, complaining about the punishment of yesterday's log race. Some of the blisters these guys are carrying cover the entire soles of their battered feet. All of a sudden, we feel nervous.

We've been "invited" to have a go at "the two-miler". It's one of Test Week's more approachable challenges, with recruits marching across two miles of rugged Yorkshire countryside (mostly up-hill) with a full 35lb kit - plus weapon, water and food - in under 18 minutes. "A nice brisk walk in the sunshine," we think to ourselves. "How hard can that be?"

Run Until We Puke
Within two minutes, we realise how very wrong we were. For a start, having the equivalent of a small child on your back makes moving anywhere at pace pretty tricky. Then there is the actual pace. "Marching" in P-Company translates as "sprinting as fast as you bloody can".

Adrenaline gets us through the first few minutes, before our legs start refusing to move. We're suddenly aware of every pound strapped to our back, the intense heat and how everything is beginning to spin.

"You're not stopping yet, ZOO!" Sgt Swindale bellows at us. As the rest of the recruits pull away, without warning, we grind to a halt and puke our guts up. Sgt Swindale is not impressed: "You're pathetic, ZOO! You're not swanning around drinking your bloody cocktails now!" After a few more choice words, we just about manage to finish the course.

Broken Noses
After being allowed a quick sit-down and shower, we're "advised" to sit out the afternoon test - the sixth in just three days. When we hear the details of the test, we can't say that we're too gutted. The knackered recruits are about to indulge in the infamous art of "milling".

Milling is a no-holds barred boxing match, where similarly matched recruits have 60 seconds to knock seven bells out of each other. There are no defensive tactics - you just charge at your opponent. One in three break their noses, we're told.

Instead, we attempt the assault course and go through a mercifully brief challenge of the log race.

Come the end of the day, we're incapable of speech and movement. Truly, this is the hardest thing you could put yourself through.

"People always ask why anyone would want to endure this," Major McGrath says as we're leaving. "But speak to any soldier and it's all about respect. Getting through P-Company means one thing: you're the best. And there's no greater feeling."

ZOO couldn't agree more.