Ireland boss Joe Schmidt believes his Six Nations champions must make a huge improvement if they are to retain the title for the first time.
Although content with an opening 26-3 victory away to Italy, the Irish coach believes England made the strongest start of all by winning in Wales.
"The benchmark was set by England. They kept the pressure on Wales," he said.
"The physical nature of that battle means we have got a bit of work to do, without a doubt."
Stuart Lancaster's England side overturned an eight-point interval deficit to win 21-16 in Cardiff.
Schmidt said his team would have to improve "between 30 and 40 per cent" from their Rome performance to stand any chance of reaching England's early level.
"We will have to roll our sleeves up and hopefully put together a sufficiently-improved performance to be competitive against France.
"We were between 30 and 40 per cent off that against Italy.
"We would not have lived with England like that. And I thought Wales were pretty good.
"For us we certainly need to up our game. I do think that part of it was the pressure Italy put on us but, at the same time, I know we can do better than that and we are going to have to."
|Ireland's 2015 Six Nations matches|
|7 February||Italy 3-26 Ireland|
|14 February||Ireland v France|
|1 March||Ireland v England|
|14 March||Wales v Ireland|
|21 March||Scotland v Ireland|
Meanwhile, Schmidt hopes unlucky flanker Sean O'Brien will be fit for the match at home to France on Saturday after suffering a hamstring injury in the pre-match warm-up in Rome.
He is also optimistic on the prospects of hooker Rory Best who was withdrawn in the second half as a precaution after taking a knock to the head.
"Withdrawing Sean was a marginal decision at the time and it was great he was able to be replaced by Tommy O'Donnell and the manner Tommy played.
"I would be hopeful, quietly confident, but we will scan him when we get back to Dublin.
"Rory's fine, he did get a knock and we decided to err on the side of caution with him as well. He will follow the return to play protocols, just because we want to be fairly careful there."