Test selection for this summer's British and Irish Lions series against South Africa is "wide open", says two-time captain Sam Warburton.

Warburton, who led the side in 2013 and 2017, said impressive performances had left 20-30 players in the Test running.

"It should be so difficult to pick," the 32-year-old told BBC Sport.

"It's going to be a more difficult Test team to pick than on any tour I've been on. It's really difficult to see how it's going to unravel because there are so many players who have done really well in their games.

"Nobody has played themselves out of contention. Everybody is still within a shout. It's wide open."

Warburton said Wales fly-half Dan Biggar and wing Josh Adams had been "phenomenal" in the opening games.

He also praised "brilliant" Scotland back row Hamish Watson, saying "those three players have stood out for me significantly".

"I think those three are frontrunners but then the baton is going to be passed over to a new group of players on Wednesday and if they have belters it is back to square one again," he added.

Boot vouchers and telegrams - Warburton's Lions Legends

The former Wales captain is hosting a special podcast series for the BBC during this summer's tour called Warburton's Lions Legends.

As well as sharing his own experiences, he will speak to some of the greatest players to wear the famous red jersey: Sir Gareth Edwards, Martin Johnson, Gavin Hastings and Paul O'Connell.

The first episode was with Edwards, who toured with the only Lions side to win a Test series in New Zealand in 1971 before forming part of the 'Invincibles' team that completed a South Africa tour unbeaten in 1974.

The former Wales scrum-half shared experiences from a tour that Warburton admits was a "world away" from his own life as a Lion.

Edwards explained that the first time he heard of the team was during news clips that would show before films in the cinema.

Rather than the live, televised squad announcements of the modern age, the Wales great says he "was sat on the stairs staring at the letterbox".

"I've never forgot this, it said 'Dear Edwards'," he recalled of the letter that eventually arrived.

"Please find enclosed a voucher for two pairs of boots. Most of the time in those days you had to buy your own boots!"

Warburton realised on his tours that players "didn't have it as hard as we thought" when Edwards said that telegrams were the only way to get quick news from back home on a trip that was more than three months long.

"It was a pound a minute for me to ring Maureen who was my girlfriend then," Edwards said.

"All I could afford was about three minutes by which time she was so gobsmacked that I rung she couldn't say anything. I was going 'Maureen, are you still there?'"

'The Lions is everyone's greatest achievement'

One thing that was shared between both Lions greats was the difficulty at being apart from their children.

Warburton toured with a one-year-old daughter back home and says he "missed her like crazy", while Edwards had to leave for South Africa shortly after his first child was born.

"My boss came out for the first Test in South Africa and brought polaroid photographs out so I could see him," he said.

"We were on the way to the first Test and I opened the letter and there was a photograph of Owen and I remember kissing it and saying, 'this one's for you'. It was an incredible feeling."

Despite Warburton's and Edwards' tours being separated by decades, both agreed that the experience of being a Lion is difficult to explain to those who have not done it.

"You speak to any Lion, they hold it in such high regard," said Warburton.

"It does not matter who you are or what you have achieved in the world, the Lions seems to be everybody's greatest achievement.

"It is the same whether you played in the 70s or whether you play now. There are so many amazing players who have got nowhere near the shirt.

"You are playing alongside heroes and legends and following in the footsteps of heroes and legends."