South Africa batsman Ashwell Prince believes England off-spinner Graeme Swann could be the difference between the teams in the Test series.
England go into the three-match series as the number one ranked Test side, with the
Prince, who was not selected for the tour, told BBC Sport: "It will be a good series and it will be very tight.
"England may have a slight edge in the spin department with Graeme Swann. He is one of the best in the world."
The seam-bowling attacks appear evenly matched - in Dale Steyn, Vernon Philander and Morne Morkel, South Africa have three players in the top 10 of the International Cricket Council rankings, while James Anderson, Stuart Broad and Tim Bresnan are third, sixth and 14th respectively - but Prince believes Swann has the edge over leg-spinner Imran Tahir.
Pakistan-born Tahir has taken just 18 wickets in seven Tests - compared to Swann's 188 victims in 44 matches - although he has enjoyed success in county cricket, chiefly with Warwickshire and Hampshire.
"Swann has a lot more experience and he also contributes with the bat," said Prince. "That is probably the one area where England have the edge over South Africa.
"South Africa's bowling attack contains the number one in the world [Steyn], number 10 in the world [Morkel] and Vernon Philander, who has burst on to the scene.
"The one guy who hasn't done as well as he would have liked coming into Test cricket is Imran Tahir, but everybody in England knows what he is capable of.
"If you look down the line-up, you can pick a match-winner from the whole XI."
Prince expects familiar faces such as Graeme Smith and Jacques Kallis to pose England problems this summer, but he has warned Andrew Strauss's men to watch out for some of the less-heralded tourists.
"When you look at a line-up you always identify the senior players like Smith and Kallis, who have been over to England a few times and done very well," said the 35-year-old.
"But there might be one or two other guys with a point to prove. They are normally the ones who come to the fore. It wouldn't surprise me if somebody like Jacques Rudolph made a big impact.
"Rudolph has had a few seasons in county cricket and has experience of playing in English conditions.
"South Africa have also got JP Duminy waiting in the wings. He got a hundred in his last Test match [against New Zealand], when Jacques Kallis was injured, so it will be tough for him if he missed out.
"If Duminy did play, he gives the team much better balance because he is more than handy with his off-spinners and he can do a job with his bowling.
"As a batsman, he won't let the team down either."
While South Africa appear to be blessed with plenty of batting options - Prince averages 42 in 66 Tests but did not make the 15-man Test squad - England are yet to find a settled number six after dropping Eoin Morgan over the winter.
Jonny Bairstow occupied that position during the series win over West Indies this summer, but scored just 38 runs in three Tests.
"The only position that England may be having second thoughts about is the number six spot," said Prince.
"They have just given a chance to Jonny Bairstow - he had a taste of Test cricket but will not be too happy with how his first few matches went.
"Whether they stick with him or go with somebody with a bit more experience, like Ravi Bopara, I don't know.
"The rest of the line-up is experienced and settled, however."
The first Test begins at the Oval on 19 July.