There is "no suggestion that Mark Harper knowingly employed an illegal immigrant", Downing Street have said.
The Immigration Minister has announced his resigned over the issue.
Number 10 said David Cameron had "accepted his resignation with regret".
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He told People Magazine: "I was in denial, but a part of me always knew this was coming."
A compound within the Conus regius snail's venom has been found to create long-lasting pain relief.
NASA says the phenomenon is "quite unusual to see".