Sir Clive Woodward believes England's clash with Ireland on Saturday will be the first major test of their world champion credentials.
Woodward is taking the Irish threat very seriously
Since winning the World Cup last year, England have not been severely tested in wins over Italy and Scotland.
"We know this is the biggest challenge since the World Cup final - there's a bigger edge to this game," he said.
"Ireland are a very strong side and we are playing our first competitive game at Twickenham since the World Cup."
The Irish have recovered from defeat by France in their opening Six Nations match - and Woodward knows the visitors cannot be under-estimated.
"Ireland thrashed Wales two weeks ago with a dominant forward display and head to Twickenham in confident mood," he said.
"We have made a few changes, some forced some otherwise and that always adds a bit of edge to the team.
"We are really looking forward to the game, the weather forecast is good and like every game at Twickenham it is just going to be a magnificent occasion. "