Stuart Lancaster has declared that the only way that England will win this year's World Cup is if they are the "fittest team" in the competition.

The Red Rose head coach announced his 50-man preliminary squad last Wednesday, with less than four months to go before they get their campaign underway against Fiji.

Lancaster intends to get every last ounce of effort out of his group during tournament preparation, which includes a two-week high-altitude training camp at a specialist rugby centre in Denver, Colorado.

"This is the one opportunity where you can [ensure they peak]. So there is no excuses in that regard," he is quoted as saying by the Daily Mail.

"In order to win the World Cup you have to be the fittest team. And the type of game we want to play [demands it]. It is probably the most important thing that we need to get right. If you are not, everything else falls apart.

"Your ability to communicate, your ability to make good decisions, and play at high tempo, all falls apart if you are not supremely fit. We've been banging the drum with our conditioning team. It is going to be pretty grim for the players in Denver. I have been there for the Churchill Cup. It is tough there."

England take on France in a home double-header in preparation for the World Cup, as well as facing Six Nations champions Ireland.