England will launch the defence of their RBS 6 Nations crown with Dylan Hartley at the helm after his ban for striking Sean O'Brien was limited to six weeks.

The length of the sanction issued by an independent disciplinary hearing on Wednesday means the Grand Slam-winning captain will be available for the opener against France at Twickenham on February 4.

Hartley was sent off for the third time in his career in the second half of Northampton's Champions Cup defeat by Leinster on Friday.

The 30-year-old had only been on the pitch for six minutes as a replacement when he struck O'Brien with a swinging right arm from behind, resulting in the Ireland flanker failing a head injury assessment.

The thee-man hearing that met in London upheld the decision of referee Jerome Garces to issue a red card, found that the offence was at the mid-range of World Rugby sanctions and chose a five-week suspension. Two weeks were added due to Hartley's poor disciplinary record before it was reduced by one week because of his guilty plea.

Before this latest red card, Hartley had amassed 54 weeks worth of suspensions for offences including biting, gouging and butting and the total for his chequered career now stands at 60 weeks.

It is the best possible outcome England could have wished for as a significant lay-off was certain, but they are now able to plan for the Six Nations knowing their skipper for all 13 victories this year will be available from the start.

The challenge facing the Saints front row is developing match fitness in the absence of any games for which he is eligible between now and the visit of France.

In the past head coach Eddie Jones has been content to propel Hartley straight back into the Test arena after significant lay-offs for concussion and a back problem, but by the time the Six Nations arrives he will have played little rugby over the past 12 months.

Jones referenced Hartley's need to improve his conditioning at the end of the recent autumn clean sweep - before his skipper had incurred his latest self-inflicted absence.

"Physically he's not at his best for this series, he's probably 80-90 per cent mark. He needs to rectify that for the Six Nations," Jones said.

The Rugby Football Union outlined its support for Hartley on Tuesday, stating that he had the full backing of Twickenham and Jones regardless of the outcome of the hearing.

"I think Dylan's got credit in the bank," RFU chief executive Ian Ritchie said.

"I think most people would say it's been a fantastic year. We've had 13 wins out of 13 and Dylan has made a huge contribution and he should be allowed to continue that.

"Dylan has clearly played a fantastic part in captaining the team, on and off the pitch just to be clear. His leadership credentials are very strong. He's made a huge contribution.

"So you view all these things in perspective and in perspective one looks at the totality of what he's done and what's happened over the years. I think we should be supportive of that."

Hartley has made only five appearances for Northampton this season - three starts and two as a replacement - due to a back problem and his involvement in England's autumn program and his next appearance in a Saints jersey will not be until late March.

Former England captain Lawrence Dallaglio accused him of "checking out" on his club, and director of rugby Jim Mallinder insists he has let Northampton down.

"Dylan's letting the team down. He let the team down at the weekend. Any time you have a sending off and it's a disciplinary matter, you're letting the team down," Mallinder told BBC Radio Northampton.

"Dylan has had a lot of criticism. I can't say I'm not frustrated about it because clearly I am. The team lost a player at 50-odd minutes when we thought we were in the game.

"We've also lost him for the next few weeks when Mike Heywood really needs a rest. The team is struggling a bit and we need some leadership from our senior players and we've lost that over the next few weeks.

"We're frustrated about that, but Dylan Hartley is part of Northampton Saints. We've supported each over the last 10 years and will continue to do so."