Warren Gatland said Dylan Hartley failed to make the British and Irish Lions squad because of the outstanding form of his England deputy Jamie George.

Hartley may be the captain of Six Nations champions England but the Northampton hooker was omitted from a 41-man squad named Wednesday by Lions coach Gatland for a three-test series against the world champion All Blacks in June and July.

Instead Gatland, like Hartley a native New Zealander, chose Ireland captain Rory Best, Wales's Ken Owens and George as his three hookers.

George's inclusion is all the more notable as he has yet to start a test for England, with his international appearances usually coming as a third-quarter replacement for Hartley.

But such has been the impact made by George off the bench for England, and indeed for reigning English and European club champions Saracens, that Gatland felt duty-bound to pick him.

"We couldn't leave Jamie out," said Gatland, who coached the 2013 Lions to a series win in Australia.

"There's a potential for him to keep improving. He's done a good job coming off the bench and is playing well for Saracens," added Gatland who, as was the case four years ago, is on secondment from his role as Wales coach.

"We felt there's continued improvement in him as a player and that Rory and Ken had great Six Nations.

"There was always going to be a tough call and someone was always going to be disappointed."

Hartley, who will now captain England in Argentina instead, responded to his Lions omission tweeting: "Head down, keep grafting, work to be done in Argentina."

And he congratulated all those selected for the Lions by also tweeting "firgun", a Hebrew word for expressing unselfish delight in other people's achievements.

England coach Eddie Jones said that he was delighted Hartley, twice a Six Nations title-winning captain, was on board for June's two-test series against the Pumas.

"We're excited about Dylan being on tour and he'll do a great job as captain. He's excited to go on the tour."

"I don't engage in any conversation about the Lions," added the Australian.

England's Jonathan Joseph, a fleet-footed centre, had been tipped to miss out on Lions' selection given his lack of physical presence.

But with powerful midfielders Ben Te'o, Robbie Henshaw and Jonathan Davies all gaining Lions places, Gatland also found room in an unusually large squad for Joseph, who caught his eye playing for England against Wales.

"We had a good discussion about the midfield and I said to the rest of the coaches that we can't leave Jonathan Joseph out," Gatland said.

"He's got some weaknesses but when I look at it from a Welsh perspective, he's the one player who causes us so many problems when we play England because of his footwork and pace."