England head coach Stuart Lancaster has warned his players they are set for a gruelling training camp as the race for spot in his squad heats up.
50 hopeful players arrived at Pennyhill Park in Surrey on Monday as the host nation's preparations for the Rugby World Cup increase in intensity.
"The players can expect a lot of hard work," Lancaster told englandrugby.com.
"They will have to train like they have never trained before.
"Club pre-seasons are equally tough but it is more the competitiveness here when you know you are fighting for that shirt.
"The first three weeks will be tough on the players. Then we go to Denver – it should get even tougher."
Lancaster stressed the work would also include leadership development and off-field activities designed to take the players out of their comfort zones.
He will also devote time to one-on-one chats with each player to give them feedback on last season and set goals and targets for the coming months.
"Ultimately it is their World Cup and they need to own the team and we want to do as much as we can to give them ownership of the team, particularly in this first few weeks," he said.
"I'm looking forward to getting going."