Martin Johnson has backed England as World Cup semi-final material if the Webb Ellis Trophy holders ''reach their full potential''.

England start the 2007 tournament from a lowly world ranking of seventh, and have already lost Jonny Wilkinson through injury for their Pool A opener against the USA in Lens tomorrow.

But victorious 2003 World Cup skipper Johnson believes England can make an impact in France during the next six weeks, despite the form guide suggesting otherwise.

Johnson said: ''It has been a difficult time over the past two or three years for England.

''But we need to have an intensity, starting against the USA on Saturday, and reach a level of execution and accuracy. Our standards must be very high.

''If we reach our full potential, then we could arrive at the semi-finals because we can beat any team when we have our game full-on.

''Regarding Jonny's injury, these things happen in sport, unfortunately.

''We wish it hadn't happened, but when it does it is someone else's turn to step up, and in this case it is Olly Barkley. I believe he will step up to the mark.

''I hope Jonny is fit for South Africa, but if he is not, then we just have to get on with it.

''It becomes someone else's responsibility to fill that role, and Barkley will be ready to play against South Africa if necessary.''

England are planning not to issue any further update on Wilkinson's condition until next Tuesday.