Abby and Brittany, who were joined by their best friends Erin and Becca, were seen boarding a London sightseeing bus, having 'high tea' and snapping photos of Big Ben and Buckingham Palace before taking a ride in the London Eye.
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Time of their lives: Conjoined twins Abby and Brittany Hensel visit London in the latest episode of their new reality TV show
'They are like two separate people, they are really nice,' two English children remarked after chatting to the girls.
The show, which debuted last month, chronicles the next part of their journey as the girls take the leap from students to young professionals via a summer travelling through Europe with their friends.
The English experience: Abby and Brittany have 'high tea' with their friends
Picture perfect: The twosome pose for photos with a friend
The girls first captivated the world in 1996 when they appeared on The Oprah Winfrey Show and the cover of Life Magazine.
Since then they have lived a quiet, normal life with their family in Minnesota, keeping away from the media spotlight until they agreed to appear on a documentary for TLC when they turned 16. The network has since given them their own show.
Row your boat: Abby and Brittany laughed with delight during a rowing lesson in Maidenhead
Two of a kind? The twins, who share one body fused at the torso, have very different personalities and tastes
But that prediction was to prove wildly wrong.
When growing up, they, like many twins, had very different personalities and tastes.
Abigail, the feisty, stubborn one, liked orange juice for breakfast, while Brittany, the joker of the family, would only touch milk.
TLC's Abby and Brittany show charts the next chapter of the twins life as they graduate from college and travel across Europe with their friends
One in a trillion: The Hensels are believed to be one of only a few sets of dicephalus twins in history to survive infancy
They enjoyed sports such as bowling, volleyball, cycling, softball and swimming.
And on their 16th birthday they passed their driving test, a mind-boggling feat of teamwork with each twin using one arm to control the steering wheel.
Speaking at the time, their mother Patty, a registered nurse, conceded that could have been a problem.
'I don't know what would happen if they got pulled over for speeding. Would they each get a ticket or just Abby because it's her foot on the accelerator?'
Feat of teamwork: The girls passed their driving test on their 16th birthday, with each twin using one arm to control the steering wheel
Speaking back then, Brittany said: 'Believe me, we are totally different people.'
It has not been unknown, however, for the twins to go out in a specially made top with two different necklines - to reflect their unique tastes - and leggings with each leg a contrasting colour and a different shoe on each foot.
Just one set of twins in every 40,000 is born connected in some way to each other and only 1 per cent of those survive beyond the first year.
Unique parenting skills: Their mother Patty has encouraged the girls to develop their own individuality and to ensure that if one of the twins misbehaves, she is careful to only scold the one responsible
In unison: The twins display an astonishing sense of co-ordination, with each using one arm to perform tasks, including playing the piano and sport
HENSEL GIRLS ARE RAREST FORM OF CONJOINED TWINS
The Hensel girls are the rarest form of conjoined twins, the result of a single fertilised egg which failed to separate properly in the womb.
They have two spines (which join at the pelvis), two hearts, two oesophagi, two stomachs, three kidneys, two gall bladders, four lungs (two of which are joined), one liver, one ribcage, a shared circulatory system and partially shared nervous systems.
From the waist down, all organs, including the intestine, bladder and reproductive organs, are shared.
While they were born with three arms, one was removed surgically.
Although Brittany - the left twin - can't feel anything on the right side of the body and Abigail - the right twin - can't feel anything on her left, instinctively their limbs move as if co-ordinated by one person, even when typing e-mails on the computer.
It is rare for twins conjoined the way that Abby and Brittany are to survive into adulthood, but despite this they are in good health, without heart defects or organ failure.
They would each have just one arm and one leg and be confined to a wheelchair.
Patty had no idea she was carrying twins until the birth at the local hospital where she worked
'The paediatrician said my babies were together but they had two heads,' she recalled in 2006. 'It was blunt, but completely accurate.
'From the first time we saw them, we thought they were beautiful.
'I kissed Abigail and then Brittany and gave them a hug. It's like that every time I pick them up from school, two kisses and one hug for the most beautiful children in the world.'
Both Mike and Patty's families have lived in a small midwestern farming community of 300 people for generations and it is here where they have brought up the twins and younger brother Dakota, 20, and sister Morgan, 18, away from the media spotlight.
What is perhaps most touching about Abigail and Brittany, however, is their ability to get on - despite their different personalities.
They seldom argue, despite Abigail always wanting to be the leader and - according to their mother - liking 'to rule the whole house'.
One twin will scratch an itch the other cannot reach or hold her hand still so the other can count during a maths lesson and when Brittany was ill with pneumonia and couldn't keep the medicine down, Abigail volunteered to take it in the hope of making her twin better.
Only once have the twins talked about separation - in childhood - when Abigail became bored and restless after Brittany fell ill with pneumonia and was confined to bed.
She started to suggest being separated from her sister, but when Brittany began to cry Abigail reassured her that everything was fine and that they'd never be parted.
Give and take: What is perhaps most touching about Abigail and Brittany has been their ability to get on, despite their different personalities