Downing Street insisted Prime Minister David Cameron had followed "proper procedures" after it emerged Friday that his Nepali nanny had been granted British citizenship.
His office said neither Cameron nor his wife Samantha had written letters in support of her application.
Cameron faced questions about his use of a foreign nanny after his immigration minister deplored the effects of Britain's "wealthy metropolitan elite" benefiting from cheap migrant workers.
Security and immigration minister James Brokenshire, from Cameron's Conservative Party, said Thursday that the rich had been the main winners from mass immigration, because they had to pay less for tradesmen and services.
Meanwhile ordinary British workers had lost out because their wages had stagnated, he said.
Britain's coalition government is struggling to paper over the cracks on immigration this week after Brokenshire accused Business Secretary Vince Cable from the Liberal Democrats of asserting "falsehoods" about the impact of immigrant labour.
Mark Harper, Brokenshire's predecessor as immigration minister, quit last month after it emerged he had unknowingly employed an illegal immigrant as a cleaner.
Cameron has employed nanny Gita Lima for several years since recruiting her through Kalayaan, a charity which helps immigrants to escape abusive bosses.
As regards her application for British citizenship, which was granted in late 2010, a Downing Street spokeswoman said: "The normal application process was followed throughout.
"As is usual, Mrs Cameron was named on her application as her employer.
"The point is that the prime minister's nanny is someone who has come here, works hard and is now a British citizen.
"You can expect that the prime minister would follow the normal process in the right way."
Asked whether Cameron and his wife had chosen their nanny on the basis of cost, the spokeswoman said: "I think they were guided by someone who would look after their children in the way they wanted to."
The statements came after Downing Street initially stonewalled questions about Cameron's nanny.
Meanwhile Deputy Prime Minister Nick Clegg -- leader of the Liberal Democrats, the junior partners in Britain's governing coalition -- was asked about his domestic arrangements by LBC radio.
"I have a lady who has a Belgian passport who helps us," he said, refusing to be drawn further.
Cable, his fellow Lib Dem, on Thursday told business leaders he was "intensely relaxed" about mass immigration and condemned "scare stories" about the issue.
Immigration is a topic which regularly tops polls of voter concerns.
Cameron wants to cut net migration from hundreds of thousands to tens of thousands by the May 2015 general election, but this target now looks highly unlikely.
In the year to September 2013, net migration increased from 154,000 to 212,000.