A VentureCo spokesman said that the injured group members were due to return to Quito by air last night.

In a statement the company said: “Our deepest sympathy goes to those involved and their families and friends.”

Mark Davison, a VentureCo director, said that the group had been just 30 minutes from its destination. The accident happened in the least dangerous, lowland part of the trip, he said.

But he added: “Any form of road travel in South America is inherently risky.

“We know this route well and we have groups there most months of the year. I think it was just an unfortunate combination of circumstances.”

The group had been taking part in the Inca and Amazon Venture and had set out on March 27. The itinerary included visits to Bolivia and Peru and a walk on the Inca Trail.

The trip began with two weeks’ Spanish language tuition in Quito and was due to end on July 10. Tickets cost £5,645 per person, including flights.

Miss Swann had been on a gap year after recently finishing a course at Henley College.

Her parents, Greg and Louise, were last night returning from a holiday in Italy after relatives broke the tragic news. Ms Swann had set off a week after her boyfriend, Harry Felton embarked on a gap year adventure in South-east Asia.

Last night his parents, Richard and Chris, were frantically trying to contact their son to tell him about his girlfriend’s death.

Speaking at their home, they said: “The family is devastated by this tragic news. We have only known Indie for about two years but she was always vivacious, witty and stylish.

“She was intelligent, academically gifted and hardworking. Our thoughts are, of course, with Greg and Louise at this terrible time.”

Miss Swann and Ms Logie had both spoken of their excitement before setting off.

Miss Swann only recently posted pictures of her and her fellow adventurers in Ecuador on the social networking website Facebook.

On March 31, her fourth day in the South American country, she wrote that she was having a “great time” and had spent the weekend in the mountains.

But on April 6 she chillingly complained about the rough bus journey she had endured on a trip to the volcano of Cotopaxi.

She wrote: “I was sick on the bus – the rockyest [sic] bus I’ve ever been on, it drove through a river!”

Miss Sadler was a pupil at the private North London Collegiate School for girls, and Miss Pincock left private Taunton School last year.

Friends of bright former school prefect Miss Pincock described the accident as a “tragic waste of a life”.

On the Bebo networking website her younger brother, John, 13, said: “Lizzie was the best sister anyone could ask for.”

Only one of those killed worked for the tour company.

Tour leader Miss Howard graduated from Durham University in 2003.

A university spokesman said: “The thoughts and prayers of the Durham University community are with her family and friends at this very sad time.”

Ms Logie’s parents, Robin and Jane, who live in Chorley, Lancashire, said that they hoped their daughter’s death would not discourage other young people from following their dreams.

Ms Sadler’s family later paid tribute to their “fun-loving and popular” daughter.

And last night Prime Minister Gordon Brown expressed his sadness at the deaths.

His spokesman said: “His thoughts are with their families and friends.”