Michelle, Sasha and Malia Obama land in UK for meeting with Prince Harry

First Lady Michelle Obama arrives at Stansted Airport with her daughters Malia, centre and Sasha. Photo / Getty Images

When the strains of raising two teenage girls while serving as First Lady get too much, Michelle Obama knows she has a place she can go to find support.

In a modest suite on the third floor of the White House lives Marian Robinson, Mrs Obama's 77-year-old mother and a bedrock of stability for America's most famous family.

"She's been that shoulder for me to lean on," Mrs Obama said. "I can always go up to her room and cry, complain, argue, and she just says: 'Go on back down there and do what you're supposed to do.'"

All three generations of the Obama-Robinson women are now in London, with the First Lady arriving at Stansted Airport on Monday accompanied by her mother and her daughters, Malia, 16, and Sasha, 14.

While President Barack Obama remains in Washington tending to trade deals and seeking allies against the Islamic State, the rest of his family will be carrying out their own form of public diplomacy in Britain.

Mrs Obama will meet be hosted for tea at Downing Street by David and Samantha Cameron and will meet with Prince Harry to discuss their shared commitment to the families of military veterans.

She will also visit the Mulberry School for Girls in east London alongside Julia Gillard, the former Australian prime minister, to promote an initiative education for young women around the world.

This way to No.10? Michelle Obama is here to promote girls' education. Photo / Getty Images

The First Daughters and their grandmother have no official role on the trip and are likely to duck out of parts of Mrs Obama's itinerary in favour of London's museums and theatres. But while they will be silent in public, the White House believes Malia and Sasha are still powerful ambassadors for the United States.

"I think the countries that we're visiting take it as a tremendous sign of respect and appreciation for the First Lady to bring her children to visit," Tina Chen, Mrs Obama's chief of staff, told The Telegraph.

Marian Robinson, sometimes referred to as "granny-in-chief", is Malia and Sasha's only living grandparent and has been a constant companion for her two granddaughters since their father first decided to run for president in 2006.

She looked after them while Mr and Mrs Obama were campaigning across the country and moved into the White House after their election victory.

Touch down for the Obama family. Photo / Getty Images

Audiences with the Pope and the Queen are just part of an extraordinary arc of life for Mrs Robinson, who never went to university and grew up as one of seven children on Chicago's poor South Side.

But the President's mother-in-law, who was still smoking as of 2012 and still does her own laundry, has never become enamored with White House life.

"She's always been able to provide a reality check on this extraordinary life that her daughter is now leading," said Peter Slevin, author of Michelle Obama: A Life.

Mr Slevin said that the First Lady was similarly trying to keep her own daughters grounded even as she raises them in a world populated by foreign leaders, around-the-clock Secret Service bodyguards and celebrity visitors to the White House.

The Obamas said last year they wanted their girls to experience working minimum wage jobs so they would understand what many ordinary Americans go through.

Both daughters must also play two sports at school, said Mr Slevin, one chosen themselves and one chosen by their mother. "She wanted them to learn how to be good at something that they did not choose."

Mrs Obama has also tried to follow her mother's example of "straight talk" with her daughters. "We talk about drugs, we talk about sex, we talk about smoking, we talk about it all," she told the iVillage women's website.
While Malia will head off to university next autumn, Sasha will be still be in senior school when her father's presidential term ends in January 2017. In an effort to minimise the disruption to his younger daughter's life, Mr Obama has proposed staying in Washington until she graduates

He would be the first president in a century to remain in the US capital even after finishing his term in office.