“I have always believed that politics is a team game, not an individual sport. Under the circumstances, I have therefore decided that the right course is for me to return to the backbenches. I am sorry for any embarrassment caused,” he said.
In his response, Cameron wrote: “I am very sorry indeed to see you leave the government, but I understand your reasons for doing so.
“In particular, I understand your view that, although you carried out checks on your cleaner, you feel that you should hold yourself to an especially high standard as Immigration Minister. You have taken an honourable decision.”
Last year, Harper had launched a controversial government advertising campaign that targeted racially mixed areas with mobile billboards warning illegal immigrants to “go home or face arrest”.
Fellow Tory MP James Brokenshire has been appointed the new immigration minister. Harper plans to continue in his role as MP.