Originally, the 2011 RBS 6 Nations champions were scheduled to play just three Tests in Durban, Johannesburg and Port Elizabeth but will now line up against sides assembled from the south and north of South Africa in Kimberley and Potchefstroom respectively.
The clash in Kimberley, against a Barbarians South XV, will take place on June 13th in between the first and second Test while they will tackle a Barbarians North outfit six days later.
"This will be a massive and exciting challenge for us," said Lancaster.
"England have never had a three-Test series in South Africa and, with two midweek games against opponents who will be desperate to impress, these five games gives us a great opportunity for a wider group of players to put their hat in the ring and gain international experience.
"We were pleased with the progress we made in the Six Nations and this tour is another important step on the journey towards 2015."