AAP

The British and Irish Lions are more than a month away from arriving in Australia, but coach Warren Gatland is already assuming underdog status for the eagerly awaited series against the Wallabies.

The Lions haven't beaten a southern hemisphere powerhouse since 1997, losing to Australia in 2001, New Zealand in 2005 and South Africa in 2009, and Gatland wasn't exactly boasting of a breakthrough performance after revealing his 37-man squad in London on Tuesday.

The Kiwi mentor was promising vibrant rugby, full houses and big profits for the code but seemed more hopeful than confident of taking the three-Test series against the Wallabies in June-July.

"The difficulty of a Lions tour is that you're bringing the players from four countries together with a limited preparation and you're playing away from home against one of the best three countries in the world," Gatland said in a teleconference to Australia.

"I think if you picked a Tri Nations team between Australia, New Zealand and South Africa and you brought them together for a few days and you went to the northern hemisphere, there's no guarantee that they would be better than the All Blacks or Australia or South Africa as individual teams.

"So that's the challenge that we've got."

Gatland, who picked 15 of the Welshman he coached to Six Nations glory this year, claimed to be "miles away" from deciding on a first-Test line-up, saying European club commitments would prevent half the tourists from even attending his squad's initial camp on May 26 - less than a week before the Lions open up against the Barbarians in Hong Kong.

"A number of positions have a huge amount of competition and depth," he said.

"In terms of picking a Test side at the moment, I think we'll wait and see how it develops."

Gatland promised everyone would have a chance during the first three mid-week games to press for first-Test selection on June 22 in Brisbane, but said the Wallabies enjoyed a big advantage.

"I'm really impressed with Australian sides at the moment," he said.

"An interesting stat when you look at Super Rugby, every time that the Lions have toured that country, that's the country that have won Super Rugby competitions.

"So it just goes to show what it means to some of those Australian players and what it means to be part of the Australian side and the Lions tour.

Gatland said he fully expected veteran flanker George Smith, a member of Australia's triumphant series winners over the Lions in 2001, out-of-favour flyhalf Quade Cooper and code-hopping revelation Israel Folau to all feature in Robbie Deans' Wallabies squad for the prestigious 2013 edition.