He is one of the greatest rugby players in the world, but Nathan Cleary has been able to walk through his Kensington hotel unnoticed this week. The place has been taken over by sumo wrestlers who are large enough to make even the biggest of rugby players look small.

Australia’s outside-half has won four consecutive NRL titles with the Penrith Panthers, amassing almost half-a-million Instagram followers. Cleary is an admirer of Harlequins and England union star Marcus Smith and the two caught up in the southern hemisphere this summer. Yet here in London, ahead of rugby league's first Ashes series since 2003, he can easily fade into obscurity.

‘We’ve been able to hop on some Lime bikes and cruise down to Big Ben,’ says Cleary. ‘We rode down to Buckingham Palace, past the Royal Albert Hall, where the sumos were doing their competition. We’re in the same hotel as them so they’ve been eating all the breakfast! Every time we’d go down to the lobby they were just sitting around, so that’s been pretty cool.’

More than 60,000 tickets have been sold for the series opener at Wembley, a stadium which would be more associated with Cleary’s footballing girlfriend, Mary Fowler, who plays for Manchester City.

League chiefs are on a mission to grow the code’s popularity in the capital, granting it the big stage of game one. In 2003 it was Wigan, Hull and Huddersfield that cornered the Ashes Tests, averaging just under 24,000 fans per game. This time, it's 90,000-seat Wembley, Everton's new 52,000-capacity Hill Dickinson Stadium and Leeds' Headingley Carnegie, which has come in for criticism as a choice given it holds under 20,000, but it will be rocking for the potential series decider.

The State of Origin series holds more weight than international fixtures Down Under but this weekend’s showdown promises to be a box-office occasion.

‘The main difference between union and league is the international stage. It’s obviously so big in union but we’re definitely getting there,’ Cleary says. ‘More countries are becoming competitive and that makes for better games.

‘To come over here and play these games, it’s a historic moment for a lot of us. Most of us were pretty young when the last series was on. I see a lot of old clips so it’s special to be a part of.

‘Not many people get to say they’ve played at Wembley so we’re very lucky. Taylor Swift was here recently. We came down to watch the NFL on Sunday and the stadium is sick.’

Cleary will feature in a star-studded Australia team alongside the likes of Reece Walsh, Cameron Munster and former union wing Mark Nawaqanitawase. On paper, Australia should be favourites, but England feature headline talent of their own, including star NRL centre Herbie Farnworth, who has been courted for a move to union.

‘Herbie’s a world-class centre,’ says Cleary. ‘He’s one of the top three centres in the game at the moment. Every time you come up against him in the NRL, you know what you’re going to get. He’s consistent, he’s fast, he’s strong. He’s got all the attributes.’

Like their union counterparts, Cleary and Co have all been put on R360’s hitlist, targeted as code-switch candidates who could sprinkle their stardust on rugby union’s proposed breakaway competition.

However, Cleary revealed to Daily Mail Sport that he has no intention to join the movement, left with little doubt after players were threatened with suspension if they enter negotiations.

‘There’s a lot of speculation about it,' he says. 'They came out with a 10-year ban if you get caught talking to R360 so I’ll be avoiding that! I don’t want to be banned for 10 years... Nah.’

With close connections between the codes, the eyes of the union world will without doubt be on Wembley this weekend.

At the start of the season, Bristol Bears coach Pat Lam named Cleary as the athlete he would most like to recruit from any other sport. England winger Dom Young previously held talks with Leicester Tigers and Australia’s Nawaqanitawase is due to switch back to union to play at the 2027 World Cup.

‘It’s not something I’d shut the door on,’ says Cleary. ‘I’m pretty open to trying different things but at the moment I’m thoroughly enjoying league. I feel I’m in a really good space, constantly getting better and really enjoying that.

‘You’ve seen a few people switch codes successfully over the time. The transition seems more seamless for the outside backs. Mark has come over from union and he’s been unbelievable.

'When he first came over, I was wondering how he’d go with the fitness and having to take a lot more carries. I’ve just found myself being a fan of him this year. Some of the stuff he can pull off is unbelievable. You see that with a lot of the union boys.’

Cleary’s 84 per cent goal-kicking success rate is as consistent as any half-back in either code. Smith spent an afternoon watching his training session in Sydney during the Lions tour, with Cleary keen to tap into the minds of some of the sharpest fly-halves.

‘I didn’t get to go to any of the Lions games unfortunately because our schedules didn’t line up, but I watched pretty much all of it and it looked incredible,’ he says. ‘Marcus came out to our training at Penrith and I got to speak to him. That was pretty cool.

‘I grew up in New Zealand so I always watched Dan Carter growing up. He’s a legend in my eyes. I’ve been lucky enough to meet him and talk with him. 

'One thing that stands out for me in union is the way they kick the ball. There’s definitely a correlation between what I do as a half-back and the fly-half in union, so I watch a lot of those guys.

‘Even though there is a lot of correlation in skills, it’s the mindset that people are trying to tap into. A lot of the time that’s the edge between good and great players. Everyone’s trying to find that edge now.’

So, which union players would Cleary like to see playing in the NRL?

‘I reckon Ardie Savea would be pretty good,’ he says of the All Black back-rower. ‘He’s a beast. The way he runs the ball, I could see him playing back row. Owen Farrell obviously had a connection to league but never got to play it. I think he would have gone well.

‘Beauden Barrett, Quade Cooper… a lot of the guys who play fly-half could go pretty well in league if they got the time to learn the game. Obviously, you get a bit more time in league, being 10 metres away from the defence, so a lot of the union fly-halves would like that.

'Sometimes I watch union and think it would be sort of difficult to get involved in the game, especially if there’s slow rucks, but all the fly-halves have elite kicking games so that would be a pretty handy attribute in league.’

As much as Cleary is interested in the union world, his focus is entirely on these upcoming Tests. It has been a long wait since their last series, more than two decades, and the grand comeback at Wembley is the perfect way to renew the rivalry.