Eddie Jones has sent his Grand Slam winners back to their clubs with the warning that none of them are assured of their places when England tour Australia in June.
Thirty-six hours after the new RBS 6 Nations champions had completed a first clean sweep since 2003 and Jones was at Leicester meeting with director of rugby Richard Cockerill and the Tigers' Red Rose contingent.
The head coach will visit all the relevant Aviva Premiership clubs with trips to Bath, Saracens and Northampton scheduled for this week.
Each player used in the Championship has been given an individually-tailored plan outlining the fitness areas and skills they must work on as Jones pursues his quest of transforming England into the best team in the world.
"All 15 places in the team are up for grabs. Everyone's got to keep improving," Jones said.
"Billy Vunipola has got to keep improving, as good a player as he was in the Six Nations. If he comes back and he's not in good physical condition, he's not mentally good, he's not going to be in the team.
"If you look at the benchmark of world rugby, the All Blacks, why did they consistently improve over eight years to win the World Cup twice? Because their players kept improving individually.
"And that's the challenge for these players. To win a Grand Slam is just a start. To keep improving is the challenge.
"Everyone wants the players to do well. We want the players to go back to their clubs and play like international players and be outstanding for their clubs.
"That'll make them better when they come into consideration for the Australia tour."
The frequently fractious relationship between club and country is often used as a reason why England have proved unable to fulfil their potential since the 2003 World Cup, but Jones refuses to view it as an obstacle.
"If you're coaching a tier one country and you don't think it's possible then you shouldn't be coaching the country," Jones said.
"Whatever circumstance you've got you've got to work out the best solution. We have a good solution here in England.
"There are high-quality clubs who are well resourced with good coaching staff, good strength and conditioning coaches and good facilities.
"If we can work with them to make sure the players are doing the things they need to do to be at their best for the club and the best for their country then we have a good solution.
"And then it comes down to whether we have enough talent and desire to do it.
"Hopefully everyone sees that England are going in the right direction and that can only be healthy for the game. World rugby is definitely healthier for a strong England side."
Jones will look closely at Henry Slade over the coming weeks after the Exeter playmaker was ruled out of the Six Nations by a broken leg and ankle injury that have healed recently.
"The guy we're interested in is Henry Slade. He gives us the option of playing 10, 12 or 13. If George Ford and Owen Farrell are fit they will definitely go on tour," Jones said.
"If Slade comes through fit then he is a definite possibility to go, but I have to see him play and I have to meet the kid to see what he is like."