UK government has given services company Capita a contract to help find and remove more than 150,000 overstayers, BBC has reported.
Chief executive of the UK Border Agency Rob Whiteman told MPs that the payment-by-results deal is worth up to £40m.
"Capita will be paid for the number of people they make contact with, and leave, and that's purely on a payment by results basis. If nobody leaves because they make contact with them, nobody will get paid," Mr. Whiteman said.
He added: "The potential value of the contract if they perform very well over a four year period would be £40m."
Some 174,000 who have been denied permission to stay in the UK have gone missing. Mr. Whiteman said he did not know how many of the missing illegal immigrants had returned to their country and how many still remained in the UK.