Harlequins' Mike Brown: I can be one of best players in world in my position
Mike Brown believes he is yet to hit his peak and can still number among the game's premier full-backs at World Cup 2019.
The 30-year-old full-back will aim to drive Harlequins into a second European Challenge Cup final in five years on Friday night, when Conor O'Shea's men face Grenoble at the Stoop.
Quins boss O'Shea will leave Twickenham for Italy's head coaching post this summer, with his charges keen to cap the rugby director's west London tenure with European silverware.
Brown faces continued pressure from Saracens' Alex Goode for his England shirt, but still reckons he can continue to thrive in the Test arena - right up to the next World Cup in Japan.
"The competition's in my head. If I keep pushing myself, I believe I can be one of the best players in the world in my position," Brown told Press Association Sport.
"I believe that, and you have to have that confidence and belief if you want to play and thrive at the top level.
"I work hard every day on the training field, hard on what Eddie (Jones, England head coach) wants me to do and what the Quins coaches want me to do.
"I do feel over the next four years I've got so much more to give and learn, and to progress.
"You've got to keep believing you can get better and I do honestly believe that.
"I've only realistically played international rugby consistently for four years, and only under three coaches.
"Eddie's come in now, it's a new perspective. The guy's been around for so many years and has worked with so many great players it's exciting to see what we can continue to learn from him.
"It's exciting to think I've got so much more to come before I hit my peak."
Harlequins lifted the Challenge Cup in 2011 with a 19-18 victory over Stade Francais in Cardiff, and will hope to contest another final this term.
But former Ireland full-back O'Shea's men must first see off Bernard Jackman's in-form Grenoble outfit.
Grenoble toppled Pro12 high-fliers Connacht 33-32 in France in the quarter-finals, and should offer Quins a stern examination in London on Friday night.
While Brown was integral to England's RBS 6 Nations Grand Slam charge, he admitted he must produce a strong finish to the campaign with Quins to cement selection for June's three-Test tour of Australia.
England boss Jones will not shy away from remoulding his Grand Slam winners, leaving Brown accepting no-one can rest on their laurels and expect to command a seat on the plane.
"Eddie wants competition in every position, he wants it three or four players deep," Brown said.
"That can only be a plus for England. If we want to win the World Cup we'll need that.
"Teams like New Zealand, when they've lost players through seasons or tournaments, the next guy comes in and is equally as good. They don't miss out on anything.
"So we need to strive to have that as well, and that means each and every one of us need to keep working hard on our game.
"I think the way we want to play with England, the players are all very excited about that.
"Hopefully we can keep honing that and bring out some flowing rugby on the hard tracks in Australia.
"We're all desperate to be on that tour.
"I've always had that goal to play in Australia, for England or whoever, so I'd love to do that.
"But there's plenty of Quins business first and I will really need to play well if I want to get picked."