London - England coach Eddie Jones believes captain Owen Farrell is "maturing at a good rate" heading into the Six Nations, while insisting wing Jack Nowell could play at openside flank.

Farrell and Dylan Hartley were England's co-captains during the November internationals.

But Saracens star Farrell is set to be in sole charge when they begin their Six Nations campaign against champions Ireland on February 2 after hooker Hartley was ruled out of the Dublin match with a knee injury.

Flyhalf Farrell's tackling technique was called into question in November, with many pundits believing he was fortunate to stay on the field after illegal 'no arms' challenges in victories over South Africa and Australia.

But Jones believes the brave and talented Farrell's game is still a work in progress.

"Owen is maturing at a good rate and he is capable of captaining the side by himself," said Jones after unveiling his 35-man training squad for the Ireland match. 

"We all want the game to be safe. I think Owen wants the same thing.

"He wants to hit people hard, sometimes he has got it maybe a little bit wrong.

"But it is not his intent and I am sure during the Six Nations he will endeavour to tackle in a legal way."

Jones has welcomed back fit-again No 8 Billy Vunipola, a team-mate of Farrell's at Saracens, to his squad.

But injuries mean he will be without Vunipola's fellow back-row forwards Chris Robshaw and Sam Underhill in Dublin.

Exeter, Nowell's club, are unlikely to uproot him from the back three to the back row and the chances of him learning a brand new position in the months before this year's World Cup in Japan appear slim - rugby league convert Sam Burgess tried something similar in the run-up to the 2015 edition when a back-row for Bath and an England centre with mixed results.

But outspoken former Australia and Japan coach Jones, was adamant Nowell could be an openside flank.

"We haven't tried him out but he is definitely an option at seven (openside)," he explained.

"He has great ball carrying, great tackling skill; he puts his head over the ball, he's a tough little bloke.

"He is going to be the new breed of player. The game has changed. The game used to be 80 minutes, now it is 100 minutes. 

"The next change is you will have players who can play backs and forwards."

But injuries in this weekend's final round of European Champions Cup pool club games could disrupt Jones' plans ahead of England's match at Dublin's Lansdowne Road.

And that is why he hasn't closed the England door on the gifted Danny Cipriani, even though the Gloucester flyhalf was again omitted from Jones' latest squad, with Farrell and George Ford his preferred No 10s.

"I spoke to him (Cipriani) this morning," said Jones. "He's got to hang in there. 

"His job is to be at his best, continue to be at his best and when the opportunity comes, be ready to go."

England finished a lowly fifth in last season's Six Nations before bouncing back to win three of their four Tests at Twickenham in November and only losing narrowly to world champions New Zealand.

"There are twists and twirls in the Six Nations as we see, so all we have to focus on is beating Ireland," said Jones. 

"What happens after that, we don't control."