Iraqi asylum seekers sent back to Baghdad by the UK government have been refused re-entry to their homeland, and flown back to Britain.
The flight, carrying about 40 asylum seekers, landed in Baghdad on Thursday. Ten were admitted but the rest were turned away and have now arrived back.
Human rights group Refugee and Migrant Justice said this was "unprecedented".
The Home Office said it was working with the Iraqi government to iron out issues that caused some to be returned.
The reason for their return, it said, was a matter for the Iraqi authorities.
It is understood that about 80 escorts were also aboard the government-chartered flight.
The asylum seekers are now at Brook House detention centre near Gatwick airport where they are being given legal advice, according to a Refugee and Migrant Justice spokeswoman.
She said: "One would have expected with such a high profile remove, the Home Office would have sorted this out with the Iraqi authorities.
"For such a high profile group to be returned is unprecedented."
She added that the reason for the Iraqi authorities turning away some of the group was unclear, but suggested it may have been that certain documents were not in order.
The government's plan to send the group back to Baghdad, where just this week at least eight were killed in attacks on a market in north-west Baghdad, met with criticism from human rights group.
There have been no returns to Iraq since 2008 and this would have been the first return to the capital city since the start of the Iraq war in 2003.
Political and sectarian violence has diminished in Iraq since 2005-07 levels, but lawlessness remains a problem, and there has been a recent spike in violent incidents.
Lin Homer, chief executive of the UK Border Agency, said: "We are establishing a new route to southern Iraq and have successfully returned 10 Iraqis to the Baghdad area. This is an important first step for us.
"We are working closely with the Iraq government to iron out the issues which lead to some of the returnees being sent back, and expect to carry out another flight in the future.
"Having an enforced route for returns is an important part of our overall approach; however the government prefers the majority of returnees to leave voluntarily."
She said more than 2,500 people have chosen to return to Iraq under the Assisted Voluntary Return Programme in the past three years and that was expected to continue.
The Home Office said it has no estimates of the current number of failed Iraqi asylum seekers in the UK, but about 1,000 had returned to northern Iraq last year, either through enforced deportation or voluntarily.