The New Zealander admits the young side still have a huge amount of work to do to be ready for Clive Woodward's men following their 23-10 defeat by Wales in Cardiff on Saturday.
But Blackadder hopes the retirements and injuries that have hit England will expose a chink in the world champion's armour despite their convincing victory over Italy on Sunday.
"England will be the ultimate challenge for us," said Blackadder, assistant to Australia's Matt Williams who saw his first game in charge end in defeat at the Millennium Stadium.
"They will pose totally different questions than Wales. They are not the World Champions for nothing.
"England have been together for a long time and Clive has been able to put all the systems he wants into place. You can't really talk about any weaknesses with them.
"But they have had a few injuries and retirements since the World Cup so maybe those coming in won't be as good as those they have replaced. We won't know that until we face them.
"We know that we have got some work to do before the game."
Skipper Chris Paterson has called on the Scottish public to show patience as the national team is rebuilt by the duo from Down Under.
The outside-half took heart from the way his side refused to buckle against Wales after they slipped 23-3 adrift early in the second half.
"We have to be honest and know that it will take time to get things right," said Paterson, who captained a team that started with three new caps in the line-up.
"It was a very difficult game for us against a Wales team playing so well. When it was 23-3 we were really up against it but we fought back to 23-10 so we should take credit for that."