Gordon Brown is standing by his top law officer despite claims that she never asked to see her illegal immigrant housekeeper's passport.
Attorney General Baroness Scotland was under renewed pressure after the housekeeper said she had never produced the document because it was not requested.
Her account directly contradicted Lady Scotland's assertion that she personally saw all of Loloahi Tapui's necessary paperwork before employing her to clean her home.
But the Prime Minister continued to back the Attorney General, insisting there was nothing in the claims that had altered his opinion.
He insisted that Lady Scotland had acted "in good faith" at all times.
Lady Scotland was fined £5,000 last week for employing a housekeeper, a Tongan national, with no right to work in the UK.
Ms Tapui and Serbian-born husband Alexander Zivancevic were arrested by UK Border Agency officers in Chiswick, south west London, on Wednesday.
She told the Mail on Sunday that her job interview with Lady Scotland had lasted just 10 minutes and had not involved producing her passport.
A UK Border Agency investigation found that Lady Scotland did not "knowingly" employ an illegal worker and had attempted to check her documents.