LONDON (REUTERS) - United, Fu Haifeng and Cai Yun stand as an unstoppable force in men's badminton doubles, hauling in four World Championships and an Olympic gold medal. Divided? One will have to fall when they meet at the All England badminton championships on Wednesday.

The duo said they would continue to play together after winning gold in London in 2012, but the Chinese have been experimenting with their line-ups and Fu is partnering Zhang Nan, while Cai is with Kai Lu in Birmingham.

The new pairs will square off against each other in the first round proper.

"The All England is an incredible tournament and everyone who plays here wants to win," said Fu.

"That is no different for me or for Cai Yun and we will both try our hardest to beat the other.

"I know all of his weaknesses because we have been playing together for years. I think that will help me, but he also knows my game very well too so it is going to be an interesting match."

While Cai was placed in the main draw, Fu and his new partner had to battle through two qualifying matches, overcoming Malaysian combination Gan Teik Chai and Ong Soon Hock first up, then beating Taiwan duo Chen Hung-ling and Lu Chia-pin.

"I feel tired after playing in two matches so close to each other," said Fu. "But I feel like I am getting used to the court and am excited to play my friend and hopefully beat him."