Third Test, (day five):South Africa 309 & 351 vs England 315 & 294 (S Africa won by 51 runs)LORD’s – South Africa captain Graeme Smith feels his side can improve further after their series win over England lifted them to number one in the International Cricket Council’s world rankings."Being number one is something we’ve pushed for, for a while,” said Smith. "We’ve achieved where we wanted to go, but we want to carry on."The challenge is the same for us as it was for England - to build a strong enough base that when the wind blows, it doesn’t blow us over.”Smith, who broke Allan Border’s record by leading a Test side for the 94th time in South Africa’s 51-run victory at Lord’s, which sealed a 2-0 series win, added: "Hopefully we can maintain these standards for some time."There are a lot of good teams around at the moment - Australia is the next challenge for the Test team, we’ve got a formidable squad here but we need a good depth of players, such as fast bowlers."Touch wood, we don’t have any injuries, but we need to have players that can come and perform at the same level. "That’s the crucial aspect of maintaining this ranking, and there’s a hope and belief that we can carry it on.Reflecting on the whole series, he added: "We’ve been here a long time, and to maintain that standard of performance from the first warm-up game to now is a great achievement from the management and the players.