Immigration officials have arrested and questioned Baroness Scotland's former housekeeper.
Tongan Loloahi Tapui, 27, was held by UK Border Agency officers in Chiswick, south west London, yesterday.
A Metropolitan Police spokesman said she was questioned over alleged immigration offences and released on bail until October.
Officials also arrested Serbian-born solicitor Alexander Zivancevic, a man she claims is her husband.
The spokesman said: "A man aged 40 and a woman aged 27 were arrested by police at an address in Chiswick on September 23 for immigration offences.
"The man has been bailed to return to a date in late October, the woman to a date in mid-October."
Earlier this week, Lady Scotland was fined £5,000 for employing a housekeeper with no right to work in the UK.
She has held on to her job despite the protest resignation of her parliamentary private secretary, Stephen Hesford, MP for Wirral West.
Prime Minister Gordon Brown has offered her strong support, stressing that she had acted "in good faith".
He said: "She has paid the fine and apologised unreservedly. I have told her of my feelings about what has happened, but I have got to ask if someone should lose their job for failure to keep a copy of documentation."
The UK Border Agency launched a probe after it emerged that a Tongan citizen paid by Lady Scotland to look after her west London home had overstayed her student visa by several years.
The investigation found that the peer had not "knowingly" employed an illegal worker and "took steps" to check the documents of Ms Tapui.
However, she was fined £5,000 for not keeping copies of those documents.
The incident was particularly embarrassing because, as a Home Office minister, Lady Scotland had helped guide the immigration law through Parliament.
She also inflamed the row by comparing her error with forgetting to pay the Congestion Charge in London.
She told Sky News: "It's like driving into the City and not paying the Congestion Charge. It's not a criminal offence."
A UK Border Agency spokesman said: "We can confirm that a woman and a man were arrested and questioned by UK Border Agency officers on September 23 for immigration offences in relation to an ongoing investigation."Reuse content