England arrived in South Africa on Wednesday with coach Brian Ashton insisting "we're not here to make up the numbers".
Ashton says players are competing for a World Cup spot
England, who will play two Tests, are missing around 35 players because of club commitments and injuries.
There have been suggestions England are heading for two heavy defeats.
However, Ashton insisted: "There have been a lot of negative comments in the press - we have addressed that. There is no negativity in this squad."
England meet South Africa in Bloemfontein on 26 May, with the second Test on 2 June in Pretoria.
There is still a lot of room to move before we finalise the World Cup squad
England coach Brian Ashton
Players from Wasps, Leicester and Bath have not been considered because of their European finals commitments, while another 10 are currently in the treatment room.
The Springboks will be high on confidence after two South African sides reached the final of the Super 14 for the first time.
England meet the Boks in the group stages at the World Cup later this year and Ashton hopes some of the players in action over the next two weeks will stake a claim to be part of the squad in France.
"This tour comes at a time where we can achieve a lot ahead of the World Cup and it was required in our World Cup build-up, as it was in South Africa's," he said.
"There is still a lot of room to move before we finalise the squad at the end of June. There is a lot of work that still had to be done within our ranks.
"There is a group of players who are out here that will be doing everything they can to make that training group and there is equally a group at home who will be doing the same thing."
Meanwhile, South Africa's preparations have been rocked by suggestions that coach Jake White's future may be under threat.
South African rugby president Oregan Hoskins insisted flanker Luke Watson should be included in a 46-man training squad, against the wishes of White.
"If (the leadership) is not happy with the coach's selections then we must change the coach," said Hoskins.
"If the administration is not happy with the situation then it must have the coach that it prefers."
White is due to cut the squad to 30 on Monday, but Hoskins would not be drawn on what would happen if Watson failed to make the cut.
"I don't want to predict what will happen. I trust that common sense will prevail."
Forwards: Alex Brown (Gloucester), Matt Cairns (Saracens), Darren Crompton (Bristol), Nick Easter (Harlequins), Andy Hazell (Gloucester), Chris Jones (Sale), Magnus Lund (Sale), Mark Regan (Bristol), Pat Sanderson (Worcester), Dean Schofield (Sale), Ben Skirving (Saracens), Andy Titterrell (Sale), Stuart Turner (Sale), Roy Winters (Bristol), Nick Wood (Gloucester), Kevin Yates (Saracens).
Backs: Anthony Allen (Gloucester), Iain Balshaw (Gloucester), Mike Brown (Harlequins), Andy Farrell (Saracens), Toby Flood (Newcastle), Andy Gomarsall (Harlequins), Jamie Noon (Newcastle), Shaun Perry (Bristol), Jason Robinson (capt, Sale), Peter Richards (Gloucester), James Simpson-Daniel (Gloucester ), David Strettle (Harlequins), Mathew Tait (Newcastle), Jonny Wilkinson (Newcastle).