BEWARE Ofisa Tonu'u - that was the warning from Wales and British Lions scrum half Rob Howley ahead of Friday night's Principality Cup quarter-final battle between Cardiff and Newport at the Arms Park.

Howley is wary of Newport trio Tonu'u, half-back partner Shane Howarth and number eight Andrew Powell, but singles out Tonu'u as the real danger man.

"It's not often you come up against a 15 stone scrum half," said Howley. "He's very important to Newport, he has formed a great relationship with Shane and we've got to stifle the 8, 9, 10, trio with Andy playing out of his skin as well.

"Tonu'u in the middle makes Newport click. He's bigger than the majority, his skills are second-to-none and his flip and reverse passes are superb. The best thing is to try to stay away from him, not look for contact and try to isolate him.

"It's a massive bonus when you've got a quality scrum half like that in your side. "No disrespect to Joost van der Westhuizen, but Tonu'u coming is probably the best thing that's happened to Newport."

Cardiff also have every respect for the way Newport have recovered and gone to the top of the league table since beating them with a young side back in early September. Skipper David Young, the former Wales captain, said: "If you look at the way Newport have improved they have been performing consistently and they are on top of their game."

Coach Rudy Joubert emphasised: "Newport have had some cracking results and have improved a lot since we beat them with a young side."

And Howley added: "They are probably the best side in Wales, playing at pace and with tempo. We''e got a good record at home but that will count for nothing.

"Newport have improved enormously, they've got that inner belief that they can beat anyone.

"It should be a great occasion and it's what Welsh rugby needs - a derby sell-out in the cup."

Cardiff lock John Tait is extremely doubtful with back spasms and could be replaced by younger brother Luke Tait, formerly of Cwmcran School. He would make his debut alongside another reserve lock in Adam Jones.