Lee Westwood admits he must keep on improving in order to fight off his challengers for the world No. 1 ranking.

17677 - I must improve to stay at No. 1 - Lee Westwood

The Englishman inherited the position in October, but soon found himself under instant pressure from Martin Kaymer and Tiger Woods.

Westwood saw off the threat with a strong end to the season - winning the Nedbank Challenge in December - but he knows he must keep moving forward to maintain top spot.

"If I can keep improving all the time, hopefully that'll be good enough to stay there," he said. "All you can do is work your hardest, and if that's good enough then that's good enough - you can't influence what other people have done."

A first major win would do much to cement Westwood as No. 1 - and he admits there will always be a glaring gap on his CV until he claims one of the game's richest prizes.

"It's the definition of every golfer's career, so it's really the only thing missing from my CV," he said. "I'd like to win one and maybe go on and then a few more. I've become world No. 1 and now it's matter of peaking for one of those four weeks - or more."

Westwood's 2011 season will begin in Abu Dhabi next month.