England captain Andrew Strauss insists his side are a long way from being the world's number one Test nation.

England, having regained the Ashes with a Test series win over Australia this summer, travel to South Africa this weekend for a tour featuring two Twenty20 internationals, five one-day internationals and four Test matches.

"It's one thing beating a side at home, it's another thing beating a side like South Africa away on their own patch," Strauss told BBC Radio Five Live.

"It's going to be a very hard assignment for us. It comes at a great time for us as a side in terms of where we are in our development.

"Potentially the next three or four months can really mould us as a side and push us a long way forward."

England have considered the prospect of being world number one and Strauss believes winning the Test series in South Africa, which begins on December 16 at Centurion, is integral if they are to achieve the ranking in future.

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"We met up yesterday and we were looking at how the rankings systems work and what it actually takes to be the number one side," added Strauss.

"It takes a huge amount of consistent performance over a long period of time, to win in different conditions, away from home, in the subcontinent and places like that - that's the only way you become the number one team in the world, by becoming really consistent over a long period of time.

"What I would say if you want to become the number one team in the world, you've got to win series like this one against South Africa."

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