England head coach Stuart Lancaster has suggested that his side's next two matches, against Wales and Australia, will define the World Cup and his career.

Speaking before England's clash with Wales in Pool A, Lancaster also pinpointed Jamie Roberts as his opposition's biggest attacking component.

"If we win the game it will be judged a success, if we lose the game regardless of what selection I made, you would all be questioning the selection I had made in the first place," Lancaster told reporters. "It will come down ultimately to the next two games. I understand the consequences and the stakes because it's the World Cup.

"There is no doubt that the way Wales attack is based around the gain line. When you're picking the backline you have to be aware of the threats they're going to bring. Wales' attacking shape is based on front-foot ball from the gainline that's nine times out of ten based around Jamie Roberts who'll either come down the 10 channel or the 12 channel.

"Wales have a strength in their defensive system and a lot of their wins are based on their defence. You have to understand how it is constructed and what it takes to break it down. It's not about playing shape out the back, it's about playing through the line."

Lancaster has picked a controversial backline including Owen Farrell, Sam Burgess and Brad Barritt.