British & Irish Lions Head Coach Warren Gatland said:
"The nature of a Lions tour means that there will inevitably be knocks which take time to recover from.
"The whole squad have worked hard but a lot of the backs have doubled up over the last two games, either starting or from the bench. Billy played well in the 1st Test for England and he provides that versatility to cover a variety of positions."
England Head Coach Stuart Lancaster said:
"All the England players and management delighted for Billy to get this great opportunity.
"He's played well for England this year, underlined that form with his display against Argentina at the weekend and goes with our full support and blessing."
The 24 year old has enjoyed a sensational first season with Gloucester Rugby since his move from the Leicester Tigers.
He earned a call up to England's Elite Player Squad for the 2013 Six Nations, making his debut against Scotland at Twickenham, scoring a try in the process.
He was then selected for the England tour of Argentina, and scored a try in the first test before today's announcement.