London (CNN) -- British Immigration Minister Mark Harper has stepped down from his post after admitting that for several years he employed a cleaner who was an undocumented immigrant.
"Mark Harper offered his resignation after he was informed that his cleaner did not have indefinite leave to remain in the United Kingdom, despite having shown him documents claiming she did," the 10 Downing Street press office said in a statement.
Prime Minister David Cameron "accepted his resignation with regret," but the statement went on to say that "there is no suggestion that Mr. Harper knowingly employed an illegal immigrant."
In a letter by Harper released by 10 Downing Street, he said he hired the cleaner in 2007 and had checked her paperwork at that time. He believed the paperwork showed she had the right to work and remain indefinitely in the UK.
Harper says a further investigation he requested since taking his current position showed the cleaner, who was not named, did not have proper paperwork.
He claims that what he did was not illegal, but undermined his authority to deal with immigration matters, and that's why he resigned from his post.
"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," Cameron wrote. "You have taken an honorable decision."