Alexander was among more than 40 foreigners arrested
An 18-year-old schoolboy is set to become the fifth Briton expelled from China amid protests at the authorities' crackdown on the Falun Gong spiritual movement.
Alexander Rostron, from Leeds, was arrested in Beijing at a Tiananmen Square protest in support of the movement on Thursday.
More than 40 foreigners were arrested and deported following the protest, in which they suddenly began unfurling yellow banners and shouting: "Falun Gong is good!" At least 30 of the protesters, most of them from the United States have since been deported.
Rosemary Katzen and Lee Hall were among four other Britons deported
Four other Britons who had planned to join the protest were detained by police in Beijing on Tuesday, and sent back to the UK after several hours of questioning.
A-level student Alexander Rostron had not been in touch with his family since the protest and his mother, Gaydor Kaye, had become increasingly concerned about him.
But the Foreign Office said on Friday that the Chinese authorities had confirmed they were holding Alexander, and would be deporting him over the next few days.
A spokeswoman added: "We have no reason to believe he is being mistreated."
A-levels
It was the biggest Tiananmen Square protest yet by foreign Falun Gong followers, and the police round-up was described as bringing chaos to the square.
Western protesters have been detained on several occasions in recent months
Ms Kaye earlier told reporters she had not wanted her son to go to China, but he had insisted. He had travelled there alone on Monday, and had being staying in a youth hostel.
She added that the Leeds Grammar School pupil began practising the Falun Gong's spiritual health exercises about two years ago.
"I get cross, because Falun Gong takes up so much of his time... I'd rather he concentrated on his A-levels," she told the Telegraph.
Britons Rosemary Katzen, 42, Lee Hall, 21, Earl Rhodes, 39, and Robert Gibson, 70, were the four Britons detained and expelled.
They said they had not broken any laws, had been manhandled by police, and had had most of their possessions taken away.
'1,900 deaths'
The Falun Gong movement, which claims millions of followers around the world, teaches meditation and exercises loosely based on eastern philosophies such as Buddhism.
It first came to public notice in China in 1992, but after attracting millions of followers it alarmed the ruling Communist party, and was banned.
Since 1999 Chinese police have rounded up tens of thousands of practitioners. Many have been sent to prison without trial - a form of punishment known as "re-education through labour".
Falun Gong claims that more than 1,600 followers have died as a result of abuse in police custody or detention centres - a charge the government denies.
In turn, Beijing says Falun Gong has caused 1,900 deaths by suicide, refusal of medical treatment, or hunger strike in detention.
There have also been several incidents when Westerners have been expelled and deported after protesting in support of the group.