Full interview on Inside Sport on BBC1 on Monday 3 September at 2305 BST
Lawrence Dallaglio admits England have not planned properly for their World Cup defence after "basking in the success" of their 2003 triumph.
Dallaglio told BBC1's Inside Sport: "The planning process for this World Cup has only just started really.
"It should have started the day after the last one. For two or three years after the World Cup we were still basking in the success of 2003.
"But I still believe we have a credible chance of defending the trophy."
Dallaglio and his England team-mates fly out to France on Monday for the World Cup and play their opening match, against USA, on Saturday.
The team have slipped to sixth in the world and are ranked as outsiders for the tournament, but Dallaglio believes they can still be contenders.
On paper we've got a much stronger team than people are giving us credit for
"We are world champions and know very definitively what we've got to do," he told presenter Gabby Logan.
"I don't think it is all doom and gloom. When I turned up in the England squad for the first time in a while (after being named in Brian Ashton's 47-man training squad in June) I was pleasantly surprised by the faces that I saw in the room.
"I looked around the room and saw Jonny Wilkinson there and thought 'you've always got a chance with him in the team'.
"I also saw guys like Simon Shaw and Phil Vickery and was pleasantly optimistic. I think on paper we've got a much stronger team than perhaps people are giving us credit for."
Dallaglio had not played for England for more than a year before being named in Ashton's training squad.
He went on to play a major role in England's summer World Cup warm-up games against Wales and France, before being named in their final 30-man squad.
The 35-year-old admits he was surprised to get the initial call from Ashton.
"It was genuinely out of the blue and has thrown the summer into a bit of chaos. Alice (Dallaglio's wife) has only just got her head round it," he said.
"I am not one who does surprises too well. Normally you plan things and have half an idea of what's going to happen. But I was ecstatic, if I am honest."
There's not a rugby match that goes by when I don't pay tribute to (my sister) and the inspiration she was to me
Dallaglio has now set his sights on a starting place against USA on Saturday.
"I'd love to be in the team - I want to start the game," he says.
"I hope we don't have anyone who is just happy to be in the squad. You have to want to be in the team."
In a wide-ranging interview, Dallaglio also talks frankly about the death of his sister Francesca in the Marchioness disaster of 1989.
"Everyone realises that at some stage things happen to change the course of your life," he says.
"There's no doubt that at the age of 16 something happened that changed the course of my life and that of my parents as well.
"My sister (who was a gifted Spanish dancer and ballerina) was far more talented than me - and I don't just say that.
"She worked incredibly hard and got to the stage where she was just about to go and enjoy it and she had her life taken away from her.
"I think that makes you stop a little bit and treat life day by day and be a little bit sceptical.
"It definitely gave me a sense of purpose in my life. There's not a rugby match that goes by when I don't reflect on that and pay tribute to her and the inspiration she was to me."