Ireland coach Joe Schmidt reckons nothing in his extensive career will have quite prepared him for the task of trying to guide his adopted country to a Triple Crown away to England on Saturday. The New Zealander is in charge of an Irish side currently eyeing a Six Nations Grand Slam after crushing Dublin drubbings of both Scotland (28-6) and defending champions Wales (26-3). But Ireland will arrive at 'fortress' Twickenham looking for their first win over England in four attempts and with the hosts themselves buoyed by a 20-0 thrashing of Scotland at Murrayfield last time out.   At stake for the Irish is the Triple Crown, the prize one of the four Home Nations -- England, Scotland, Ireland and Wales -- gets for beating all the others in a single Six Nations season. Twice a European Cup winner when in charge of Irish province Leinster, Schmidt was under no illusions about the difficulty of trying to steer Ireland to their first victory at Twickenham since 2010. "There have been some challenges that would stand out in my mind but none as tough as this," said Schmidt. The coach has been able to name an unchanged side from the team that overpowered Wales thanks to the work of such physically uncompromising forwards as Ireland captain Paul O'Connell and blindside flanker Peter O'Mahony. But England, whose pack includes captain Chris Robshaw, Billy Vunipola and Courtney Lawes, are no slouches up front either. "The way we've been playing in recent times, particularly our last three games, we've been good," said O'Connell. "But in physicality, fitness and mental stakes the step up is huge," the Munster lock added. Behind the scrum, Ireland boast several more Lions, including half-backs Conor Murray and Jonathan Sexton. But, as has so often been the case, there will be plenty of attention on Brian O'Driscoll. - 'Phenomenal Professional' - The Ireland centre, fit following a stomach bug, will equal former Australia scrum-half George Gregan's world record of 139 caps on Saturday in what will be his final international at Twickenham before he retires at the end of the season. "Where I grew up, in a black (New Zealand) jersey it would have been phenomenal, so how you manage to amass 130 of them, I'm not quite sure how you do it," said Schmidt. "You have to be incredibly resilient, incredibly talented, a phenomenal professional, and there's your summary: that's Brian O'Driscoll," added Schmidt, who coached the Irish hero at Leinster. England coach Stuart Lancaster was equally well aware of O'Driscoll's class but warned against concentrating too much attention on the midfield maestro. "He's a key cog in the team, but there are other key cogs, the half-backs are excellent, Paul O'Connell in the second row, (Jamie) Heaslip at No 8 , the list goes on of experienced players who make that team tick." Lancaster has been forced into making a change, with the fit-again David Wilson, who has played just 47 minutes of rugby during the past two months, all of it during Bath's 27-23 English Premiership victory over Exeter on Saturday, replacing Dan Cole after his fellow tighthead prop suffered a season-ending neck injury. "David has been fantastic in training this week and is ready to play, so there's no concern about him," Lancaster said. "He's an excellent tighthead and is experienced too." Lancaster has also made a change on the bench, selecting uncapped 20-year-old Bath fly-half George Ford as specialist cover for first-choice No 10 Owen Farrell. "If he does get his opportunity we know he's ready," Lancaster said of Ford. "George is composed and controlled and his confidence has grown throughout the season for Bath." As for the match itself, where two powerful packs will try to establish supremacy so as to release the attacking backs on both sides, Lancaster said: "Ireland are a very good package now and are very confident. It will be a big game." Source: AFP