Alastair Cook has insisted he is not panicking about his inability to score a century as he prepares to open the batting in tomorrow's third Test against South Africa.

The 23-year-old Essex left-hander found the transition from the county game to international cricket relatively easy after scoring seven centuries in his first 24 Tests.

But ahead of his 33rd Test for England at Edgbaston, Cook is facing the first potential crisis of confidence since making his debut against India in Nagpur two years ago.

He has not scored a century since hitting 118 against Sri Lanka in Galle last December and, more frustratingly still, he has passed 50 four times in that period without being able to convert into three figures.

"It's disappointing to say the least," admitted Cook. "Graham Gooch always told me the first 50 is always the hardest and after that it should get easier.

"It's frustrating for me at the moment because I keep getting out and not getting hundreds.

"I've always scored hundreds so far in my career as an Essex and England player, so I'm not worrying too much about it."

Cook was one of the few batsmen who could leave the second Test defeat at Headingley with his head held high after battling for over four hours for 60 during England's doomed attempt to save the game.