England's Six-Nations rugby form has caught the eye of All Blacks coach Graham Henry.

Henry has been watching Martin Johnson's men closely during their campaign, which concludes against Ireland on Sunday morning (AEDT).

Victory at Dublin would secure England the grand slam and Six Nations title, but, win or lose, Henry believes England, who won the Australia-hosted World Cup in 2003, will be a threat when the World Cup rolls around in September-October.

"I think England are developing into a pretty powerful unit, and I think they'll be very competitive come World Cup time," Henry told reporters on Wednesday.

"They're the best of them (northern hemisphere teams) at the moment, but they've all got the potential to play well."

France have been at their inconsistent best and sunk to a new low with a 21-22 defeat to Italy at Rome last weekend, but Henry knows better than to write off a French team, no matter how they are playing six months out from the New Zealand-hosted tournament.

France beat New Zealand 43-31 at London in the semifinals of the 1999 World Cup after suffering a 7-54 defeat in Wellington earlier that year, and in the 2007 World Cup the Tricolours also defeated the All Blacks, 20-18 at Cardiff in the quarter-finals, after being thrashed 3-47 on home turf in Lyon the previous year.

"I can't remember the result in 2007 when we played them," Henry said with a straight face, "but that may be some sort of indication about the French.

"They'll bounce back and they'll play well in the rugby World Cup."

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