NO-NONSENE referee Wayne Barnes will be in charge of Worcester Warriors’ must-win Aviva Premiership clash at London Irish on Sunday (1pm).

It will be the 162nd Premiership match for Barnes, who sent off vastly-experienced Warriors lock Donncha O’Callaghan for the first time in his career in December.

Warriors know Barnes will set out his stall early and clamp down on ill-discipline, particularly at the scrum, so the visitors will need to boss that battle at the Madejski Stadium.

O’Callaghan was dismissed early in the second half of Warriors’ 29-20 loss to Leicester Tigers in December after they had roared into a 17-0 lead and held a 17-7 advantage at the break.

The former Munster star picked up two yellow cards, while Matt Cox and rookie prop Gareth Milasinovich were also sent to the sin-bin by Barnes.

Barnes yellow-carded Harlequins duo George Lowe and Jamie Roberts when he officiated in Worcester’s 24-20 bonus-point reverse at Sixways last month.

Cork-born lock O’Callaghan, who turns 37 in March, is enjoying the challenges which the Premiership has thrown up.

“It’s very different from the PRO12,” said O’Callaghan who joined Warriors in the autumn after 94 appearances for Ireland and a glittering 17-season spell with Irish giants Munster.

“The Premiership is very direct and very physical and your weaknesses get rammed down your throat.

“If you are a poor defensive team that will come at you and if you are poor at kick retreat, a team will highlight your weakness and really expose it.

“It’s a lot more physical and maybe in the Pro-12 there’s a greater interest towards playing towards space and exposing inside shoulders or playing certain patterns that will expose a blindside or open side. Here, it’s coming right over the top of you for 80 minutes.”

O'Callaghan represented the British and Irish Lions on their 2005 and 2009 tours.

He was part of the Munster squad who lifted the Heineken Cup in 2005/2006 and 2007/2008, while he won the Grand Slam with Ireland in 2009 and secured four Triple Crowns.

In March 2014, O'Callaghan made Munster history when he came off the bench against Zebre to earn his 241st cap, overtaking the record for club appearances held by Ronan O'Gara.

He said: “For a front five forward I love the physical side but if I was sitting in the stand I enjoy seeing talented backs like Ryan Mills and I want to see these guys with the ball.

“As a front-five forward, it’s physical and I have never played in a tougher league. It’s scrum, maul and breakdown and you have to be brilliant at it every time.”

Warriors are 10th in the Premiership with just two wins under their belt but O’Callaghan believes Sixways could be a “special place.”

“I think this could be really good and a special place,” he said.

“I know there’s buy-in from the players and buy-in from the coaches.

“We need a collective pull together and make the place a bear pit so teams don’t want to come here.”