The boost came after national coach Stuart Lancaster waived his right to demand they be rested.
The Rugby Football Union's deal with Premiership Rugby includes an agreement for England players to be given one weekend off in preparation for the Six Nations campaign.
The elite player squad (EPS) rest window covers last weekend's European fixtures and the next two rounds of Premiership action, around Christmas and New Year.
But Lancaster, England's interim head coach, and RFU professional rugby director Rob Andrew decided not to enforce the agreement this year.
Andrew said: "We decided that given the clubs were without their World Cup players for a substantial period up to and during the tournament it was right that the EPS period should be waived over what is a crucial European and domestic rugby period."
Lancaster will name England's 32-man Six Nations squad on January 11 - and it could feature 17 names who did not play at the World Cup.
Under the terms of the agreement, England can make a total 10 selection changes to the 30-man World Cup squad and replace those who have retired or have long-term injuries.
England have five players in those brackets - Lewis Moody, Steve Thompson and Jonny Wilkinson have all quit Test rugby while Andrew Sheridan and Richard Wigglesworth are both recovering from operations.
On top of that, Lancaster can draft in two more names to complete his 32-man Six Nations squad.
England will also be naming a Saxons squad on January 11 and it is understood Lancaster has asked the red rose medical team to track a total of 94 players.
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