"My life has changed unbelievably," Delon Armitage says as he remembers that, exactly a month ago yesterday, he made his debut for England against the Pacific Islanders. "The difference between me on November 8 and now is huge. It's the difference between a guy with lots of doubts beneath the surface and a player who believes he's got the complete trust of his manager and coaches. I've now got real belief in myself."

Armitage grins helplessly as his pride lights up a murky morning at London Irish's training ground in Sunbury. During a miserable November for English rugby, a win on Armitage's debut over a patchwork side was followed by defeat to Australia, humiliation against South Africa and a vaguely more dignified pounding at the clinical hands of New Zealand. The fullback's vivacity and assurance stood out amid the dejection as he emerged as one of the few reasons to argue with any ­conviction that England's decline might be merely temporary.

There are still areas of weakness in his game but his enthusiasm is sharpened by a composure which suggests he has the aptitude to succeed in Test rugby. Even more impressively, Armitage sounds steely when reflecting on the autumn internationals. "Losing in an England shirt, at Twickenham, is just the worst thing," he says pointedly. "Growing up in France I learnt one thing above all else as a rugby player: losing at home is not acceptable. You should never lose at home."

Armitage's French experience between 1996 and 2002, arriving in a new country at the age of 12, was formative. His English step-father, John Armitage, accepted a job in IT in the south of France and he took his Trinidadian wife and her five sons to Roquefort-les-Pins, near Nice. Delon and his older brother, Bevon, who had both started playing rugby in Wembley, joined Racing Club de Nice. Although Delon insists Bevon was the better player, the younger Armitage was soon invited to ­trials for France Under-16s.

"They called me 'Rosbif' and the whole rugby culture was an eye-opener. At Nice, before a home game, the forwards would head off to the showers and us backs would move to a safe place. They'd come out a few minutes later, blood streaming down their faces, because they had been head-butting each other to psyche themselves up. They were 15!"

Armitage shakes his head. "There was so much passion that even when we played Under-16s against Toulouse, who had stars like [Frédéric] Michalak and [Yannick] Nyanga, we never lost at home. We might ship 60 points in Toulouse but at home we were virtually unbeatable. I guess that's why, even after England lost by almost 40 points to South Africa, I still thought we should beat New Zealand at home."

Before reverting to England's current travails, Armitage uses his French ­adventure to explain why he felt such gratification to finally play Test rugby. "When I was called up to those Under-16 trials I started to think how much I'd love to play for France against England. I got to wear the French national jersey in a trial game against Spain. But it was my last game for them."

Armitage turns 25 on Monday, a relatively mature age for an emerging rugby international, but the hurt he felt at 16 almost ruined his career. "I've still got that French jersey but what they said afterwards nearly finished me. They said I was too small and skinny to ever make it. The other guy they bumped was Nyanga. He's obviously bulked up a lot to become a Test flanker but he was also told he was too small. I don't know how it affected him but I was devastated. For a year after that I never went near a rugby field. I was so ­gutted with rugby I turned to football."

He pauses for breath, as if still startled to think he might never have played rugby again had it not been for a junior tour that caught his step-father's eye. "I'd played for Richmond before we moved to France and my dad heard about this tour they were going on to Australia, New Zealand and Fiji. My dad said you can't miss that. I wasn't sure about playing rugby again but I thought, 'Well, at the worst, I'll have a great holiday.' So off I went with Richmond and, before I knew it, I was enjoying rugby again. My coach at Richmond said I should come back because, if I did, I would play for ­England. And here I am today — talking to you about doing that very thing."

Armitage admits that he devoured the mostly effusive newspaper reports about his first four Test performances. "I was very happy to read all that was said about me but, at the same time, I'm a team player. Those words don't feel quite so sweet when I'm part of a struggling team. But we're young and we need to execute better. We had a lot of chances we should have taken."

The full-back came closer than anyone to scoring a try against South Africa when his run to the corner flag was only blocked by a combination of the huge Springbok lock Bakkies Botha sprinting almost 50 yards across the field and a big hit from JP Pietersen. The immense fitness of Botha appeared to epitomise the gulf between two hemispheres.

"That match was the most physical game I've ever played. The pace, skill and intensity of the southern hemisphere is at another level. But we can match them if we put in the work. I'm actually excited about England's chances in the Six Nations. It's going to be tough, but we want to win the grand slam. And there can be no more excuses because we used them all up in the autumn. We can only look ahead and work extra hard."

The additional training Armitage has put in over the last two seasons at London Irish with Mike Catt and Toby Booth has transformed him — and he is unstinting in praising his two mentors and a club which leads the Premiership. Booth, Irish's head coach, has decided to save Armitage's club return for a top-of-the-table clash a week on Saturday against Gloucester. "They're very thoughtful and encouraging — just like Martin Johnson at England. He's been amazingly supportive and helped my confidence hugely. Martin's the kind of guy you can talk to about anything and he knows just the right thing to say — whether it's checking how you're feeling or what he wants you to do to improve your game. Each week he gave me such belief."

That surging confidence was missing in the haunted days leading up to Armitage's debut. His describes his emotions candidly. "I came out of a very bad patch when I got picked for the senior squad. Last summer had been devastating because I had set my heart on making one of the England tours but I broke my toe in the Heineken Cup. [His younger brother] Steffon got picked for the Saxons which cheered me up a bit — but I was still depressed. I looked at all these full-backs who had already been chosen for England and Mike Brown, Nick Abendanon and Olly Morgan were all younger than me. They looked like the future for England — which was hard to take.

"But I worked hard and when the call came from Martin it was overwhelming. You spend your life hoping and praying you will make it and when it happens…I dunno… I was so shocked. I started thinking, 'Am I really good enough?' On the morning of my first Test I started panicking, feeling sick to my stomach. I couldn't go down and eat any breakfast. I got a protein shake down me but I still felt too sick for lunch. I was a mess. With about two minutes left in the dressing room I thought, 'OK, this is probably the only time you will ever wear an England shirt. You might as well be decisive and do everything 100%'. That calmed me and as soon as the whistle went they sent up a high ball that I caught cleanly and, bang, I was away. I suddenly felt right at home."

England could do with more of Armitage's honesty and subsequent poise — and they can be relieved that Delon is likely to be only the first from a large family to play international rugby. If his eldest brother's hopes have been ended by injury, the upcoming trio of Steffon, the 23-year-old flanker who is a key figure at London Irish, 16-year-old Guy, a star at the club's academy and 13-year-old Joel, a try-scoring prop, could all follow Delon. "Steff is really close," Armitage says. "He's just won the Premiership's player of the month. It is our dream to play together for England and if he goes on like this he'll make it hard for them to leave him out the squad."

One Armitage is not quite enough to signal an England revival. But two brothers, born in Pepper Village in Trinidad, and raised in French rugby before flourishing with London Irish, could begin a family legacy that might coincide with a worldly renaissance for English rugby. "I've got some very talented brothers and I'd love them to play for England," Delon says, "but we've all got a long way to go. I got here first and I intend to make the most of my chance. I finally feel like this is where I belong."