Cameron's Downing Street office said in a statement released Saturday afternoon that there was no indication that the minister, Mark Harper, knew the cleaner was working illegally but said the leader accepted the resignation "with regret."
No further details were available, but the fact that a top politician, one charged with policing immigration, no less, had an illegal employee is likely to dominate the headlines.
One of Cameron's central campaign promises involved a clampdown on illegal immigration, and he's been repeatedly challenged by the right wing of his party on the issue.
