England captain Martin Johnson does not expect the Twickenham fortress factor to have much of a bearing when his team face "the strongest Irish side I've ever played against" on Saturday.

England have won 13 matches in a row at HQ - four short of the world record - since New Zealand beat them in a World Cup group match in 1999, and their supporters have become used to success.

But Johnson, responding to suggestions that home advantage is worth a start of several points to England, insisted: "It's only because we have played well at Twickenham that we have won games.

"Every team plays better at home but if we go out and miss tackles and turn the ball over we will be behind, whether we are at Twickenham or not.

"It's only an advantage being at home if you play well."

Johnson put his own pending disciplinary problems, following the much-studied punch on Saracens hooker Robbie Russell, to one side to focus on the challenge facing England.

Although Saturday's team will contain only five members of the side deprived of last season's Grand Slam by Ireland's 20-14 victory in October, Johnson still believes it is important to consider what happened at Lansdowne Road.

"It's quite amazing that in only four months there have been so many changes, but there is still a lot of relevance to that game. We have to learn from it and try and counter the things they do well," he said.

Just as the contribution from his club side at Leicester is a big influence in the England pack, Johnson knows just how important the Munster effect is for the Irish.

"I watched Munster play at Stade Francais and it was one of the best wins in European Cup history," he said.

Johnson and those England team-mates who went on the Lions summer tour to Australia have no excuse not to be fully aware of the danger posed by Irish centre Brian O'Driscoll.

"It was obvious anyway but you know him a little bit more as a player, what he does, how he runs. The Lions tour has one of the biggest exposures in world rugby so everyone knows what he can do," he said.

But, despite the absence of Ireland's talisman captain and hooker Keith Wood, Johnson is fully aware that the danger could come from almost every part of a fired up Irish side.

He singled out his Leicester team-mate Geordan Murphy on the wing, but also fears the damage which could be done by goal-kicking outside-half David Humphreys who, said Johnson, is "playing some of the best rugby of his life."

The captain makes no secret of his belief that England will have to step up a level from their victory over Scotland in the opening Six Nations match at Murrayfield a fortnight ago.

"To win by 26 points away from home and score four tries, you have to be very happy with that, but there were certain parts of the game where we could have played better."

Saturday, he readily accepts, will be much tougher.

"We will have to be better than we were against Scotland," he said.

"Ireland have beaten France and Wales, ran the All Blacks close and played to their strengths.

"They certainly did that when they played England at Lansdowne Road. Their defence was more disciplined than it has ever been and they are a great attacking side.

"We need to be on our toes or they will be through."

It all adds up to being a classic encounter and Johnson added: "It could be three points, it could even be a one point game."