Ireland celebrate after scoring the fourth try which secured a bonus point against Scotland

Former Ireland fly-half Tony Ward believes the completion of a Grand Slam against England at Twickenham would represent "the greatest achievement in the history of Irish rugby".

Ireland's win over Scotland on Saturday and England's subsequent defeat by France ensured a third Six Nations win in five years for Joe Schmidt's side.

"I honestly believe that if we beat five teams in a seven-week period in a year when we were away to France and England it would surpass anything that has gone before," said Ward.

"Up to this point I think beating Australia in the World Cup in 2011 is our greatest victory because of the context of that match but if we could beat England at Twickenham that would provide the most incredible springboard going forward to the 2019 World Cup.

"Winning the championship is fantastic but if we were to lose next week I think it would take away somewhat from what we have achieved so far," added the 19-times capped international.

Rory Best says Ireland will have to 'dig deep' to complete Grand Slam at Twickenham

Ireland focused on a 'clean sweep'

The ex-number 10 is pleased that Ireland are not resting on their laurels after an 11th successive win but are firmly focused on capturing just a third Grand Slam success in their history.

"[Ireland captain] Rory Best has said that we have got to dig deeper than ever against England and that's a brilliant attitude," said Ward.

"Johnny Sexton made a similar comment when he said no-one was jumping around in the dressing room, basically indicating that no-one was celebrating a win yet but we'll do that on Saturday if we achieve the Grand Slam.

"We've won four games out of four but even coming away on Saturday there was a feeling that we are still not playing to our optimum ability. That's how I feel and that's how I see it.

"There are periods in the game where we are delivering and where we are stringing phases together and playing error-free rugby but I can't honestly say that we have done that enough in any one game, yet we have won all four."

Stockdale impact 'Roy of the Rovers' stuff

Ulster winger Jacob Stockdale's two tries in the 28-8 triumph over the Scots took his tally to 10 in just eight international games, a breakthrough which Ward says has given everyone who supports Ireland "a feelgood factor".

"To think that this is Jacob's first season of international rugby - it's 'Roy of the Rovers' stuff. His reading has been absolutely superb and he has taken that to a new level.

"He has been absolutely brilliant and let's enjoy what he is doing at this point in time. It is wonderful.

"Allied to that we have at the moment I think the best half-back combination in the world as a collective in Sexton and Conor Murray.

"After injuries cost us so dearly at the 2015 World Cup, Joe decided that we needed three for every position and you have to say he is getting there in achieving that."

Ireland remain unbeaten in the Six Nations at the Aviva Stadium in Dublin under Schmidt's tenure and Ward credits the New Zealander's much-vaunted attention to detail as a major factor in maintaining that record.

"Joe is a workaholic, a control freak, but a brilliant communicator and a brilliant reader. I think he is the best coach in world rugby at this time.

"He takes each game on its individual merits and treats it on a 'horses for courses' basis which I think is exactly the right approach."

Tony Ward was speaking on Radio Ulster's Sportsound programme and is part of their Six Nations coverage.