Watching Ronan O'Gara boot Ireland to Grand Slam glory fixed James Ryan's resolve to chase a Test rugby career.

A 12-year-old Ryan looked on in awe from the Principality Stadium stands as fly-half O'Gara's last-gasp drop-goal sealed Ireland's last Six Nations clean sweep, with a tense 17-15 win over Wales in Cardiff in March 2009.

Fast forward nine years and Ryan will put his 100 per cent Test match victory record on the line as Ireland seek just their third-ever NatWest 6 Nations Grand Slam when facing England at Twickenham on Saturday.

Ryan's ultra-fast maturing process has left even Ireland boss Joe Schmidt calling the 21-year-old "Big Cheese", and now an eighth-straight Test win would carve the Leinster lock's name into national folklore.

"I was in the stadium and facing O'Gara as he hit that drop-goal," said Ryan, of Ireland's 2009 Grand Slam triumph in Cardiff.

"I was with my family; it was incredible. It was my first time in that stadium, and we travelled over in the morning.

"It was one of my most memorable days as a kid.

"Watching that success definitely played a big role in my decision to try to become a rugby player. Every success, Leinster winning Heineken Cups, Ireland winning the Grand Slam, it all played a part."

Just last season Leinster sent Ryan on loan for game-time in the Munster A team; in less than 12 months he has made his Test debut, and helped Ireland claim a third Six Nations title in five years.

Ryan has long been earmarked for Test status, only for a string of niggling injuries to dent his progress. But to be trusted to start a Grand Slam decider as a 21-year-old lock only serves to underscore his startling proficiency.

Schmidt, meanwhile, has hit back at Matt Williams, insisting there would be nothing "boring" about leading Ireland to just their third-ever Grand Slam.

Former Leinster and Scotland coach Williams has been unimpressed with Ireland's rugby despite Schmidt's men claiming a third Six Nations title in five years.

Williams launched his latest criticism of Schmidt after last weekend's 28-8 win over Scotland, and despite Ireland chasing a Grand Slam to stand alongside the triumphs of 1948 and 2009.

Victory over England at Twickenham on Saturday would cement Schmidt and the class of 2018 in Irish folklore, and Ireland's Kiwi boss insisted he will not fret about style points in London this weekend.

"We don't want to be described as boring, but I don't think any of the team would care if it was 3-0," said Schmidt.

"I don't think we would be uninspired by a 3-0 victory, because we know what's at stake.

"And what's at stake is a fantastic opportunity not just to achieve a Grand Slam, but to go a year unbeaten – we wouldn't have dreamed of that this time last year."

Schmidt and Williams have regularly traded barbs in recent seasons, with the Australian coach continuing to act as a pundit on Irish TV Six Nations coverage.

Ireland racked up an all-time record 11th consecutive victory by seeing off Scotland last time out, leaving Schmidt nonplussed by Williams' criticism.

That unprecedented sequence of results started with Ireland denying England the Grand Slam with a 13-9 win over Eddie Jones' side in Dublin on the final weekend of last year's Six Nations.

Schmidt believes Ireland have built steadily since, and has challenged his side to realise that progress with a first victory at Twickenham since 2010.

"This time last year we were scrambling around, we thought Conor Murray was going to play on the Thursday, and Kieran Marmion came in and did superbly," said Schmidt.

"And Jared Payne played his only game of the Six Nations.

"That character reference that we have from that group, has helped us build from there on.

"And hopefully we can continue to build on that, and that would be special for us in all sorts of ways, because of the championship and what is at stake."