The RFU has just announced a major law change:

The intention of the new regulation is to minimise the occurrence of uncontested scrums. The RFU has now adopted what is known as the “Man Off” Rule.
Once a referee has declared that scrums will be uncontested because there is no suitable front row replacement for a suspended front row player or a front row player who is injured (other than a blood injury) to enable scrums to remain contested safely he will ask the team captain from the team which has failed to provide a suitable replacement to remove one additional player from the field of play immediately.
In the case of an exclusion for disciplinary purposes causing uncontested scrums the removed player will be in addition to that player excluded. On return to the field of play of any player who has been temporarily excluded (i.e a yellow card), any additional player who has been withdrawn may also return and fully contested scrums shall resume.
In the case of a temporary blood injury to a front row forward causing uncontested scrums no additional player will be removed. He can be temporarily replaced by a non front row specialist and the game continued with uncontested scrums for up to 15 minutes. On return to the field of play of any player who has been temporarily injured subsequent scrums shall revert to being contested.
In the event that the front row player who leaves the field of play through a blood injury does not return within 15 minutes thus enabling scrums to be contested he will be deemed to have been permanently injured. The referee will then ask the team captain to remove an additional player and the game will continue with uncontested scrums until its conclusion.