Willie Mason admits he's way out of his comfort zone but welcomed the challenge of starting his code switch to rugby union against England at Twickenham.

Mason has been named on the Barbarians bench as a centre reserve for Sunday's showpiece match - his first in the 15-man game since his Auckland high school days in 1997.

The colourful 31-year-old former NRL forward, who played 24 times for Australia between 2002-08, has been lured to union by big-spending French club Toulon.

A clash with England's second string is hardly the kindest of reintroduction to rugby.

"It's a pretty big debut - against England at Twickenham, which is normally the highlight of your rugby career for many people," said Mason.

"I haven't been this excited about a game for a while.

"I'm way out of my comfort zone. I have thrown myself in at the deep end and I just can't wait to get out there and do it.

"I've played in plenty of big games before, it's not like I'm someone who doesn't know how to catch a ball, run, or tackle, which are the basics of rugby.

"Obviously I'm not going to go into the game thinking I'm going to get man of the match or anything, but I've got high expectations of myself as a player and a competitor.

"I'll hold my own regardless if I'm playing a national side like England, which I have full respect for. But I am a competitor myself."

Mason has a chequered disciplinary history and was voted the National Rugby League's most hated player by a fans pole in 2007.

His reputation also suffered at UK Super League club Hull KR, who last weekend released the controversial signing just six months into his three-year contract.

Patchy form in his six appearances for the club, the revelation he met officials from Toulon without permission and passport issues resulted in his acrimonious departure.

Toulon, who are reportedly paying him STG395,000 ($A612,000) a year, have taken a considerable gamble on a player who joined Rovers after failing to find an NRL club.

"I had a choice when I first came out of high school to play union or league," said Mason.

"Rugby league is a major sport in Australia and that's the way I went. I don't regret that.

"I played 12 years in league and achieved everything and I've been pretty happy with what I've done over there.

"I've always had the opportunity to come to rugby union but I've always chickened out at the end.

"I've had numerous meetings with (former Australia coach) Eddie Jones and the Wallabies two or three times during my NRL career, but always chickened out.

"Now I'm here and made the switch and I'm happy."

Mason, who played prop in league but has been earmarked for the centres in union, admits Sonny Bill Williams played a key role in his change of codes.

League convert Williams is set to feature for the All Blacks at the 2011 World Cup after being thrust into the limelight by a successful two-year spell at Toulon.

"We played the same position in league and we won a lot of things and played against each other. We're good mates," said Mason

"Sonny has probably opened up a lot of doors for me. I don't think I'd have been given this opportunity if Sonny didn't open those doors up initially.

"Couple of years ago he said, 'Right, I'm going to union'. He made a harsh decision.

"Bulldogs fans weren't happy with it but they don't like me or him so we're in the same boat there. We have done everything together.

"I've been talking to him and asking him what the transition is like mentally, physically, what you do on the field and all the variables in the game that you have to get used to."

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