The 26-year-old man, who has not been officially named, was on a flight that landed at Heathrow Airport on Thursday afternoon.
A spokesperson for the Metropolitan Police said: “He was arrested on suspicion of preparation of terrorist acts under section 5 of the Terrorism Act 2006. The arrest is Syria-related.”
The man remains in custody as the investigation continues.
He was one of several alleged British Isis supporters held in Turkish prisons, where Aine Davis – a member of “The Beatles” terror cell – was jailed after a 2017 trial.
The offence of preparing terrorist acts is levelled against people accused of travelling to join Isis, as well as for those plotting attacks.
Turkey announced the deportation earlier in the day, alongside that of several German Isis suspects.
Ankara has, this week, accelerated a push to deport suspected foreign Isis fighters held in prison to their respective countries, a move that dovetails with Donald Trump’s demands that European countries take back and try militants caught in the battlefields of Syria and Iraq.
Kurdish forces that were backed by the US-led coalition – to push Isis out of its “caliphate” – are holding tens of thousands of people, caught fleeing the terrorist group’s territories, including foreign fighters from around the world.
The Syrian Democratic Forces (SDF) has warned that it may not be able to secure the camps if Turkey continues an advance into northern Syria, and said it was the “moral and legal duty” of the UK and other countries to repatriate their citizens.
The British government has dramatically increased its use of controversial citizenship deprivation powers in attempts to prevent Isis members from returning to the UK.
The government has repeatedly refused calls to repatriate British men, women and children held in Syria, arguing it is too dangerous for officials to undertake the task.
But it cannot prevent UK citizens from seeking consular assistance if they manage to leave the war-torn country.
The Home Office has previously confirmed that British nationals have the right to return to the country but they will be investigated by police and authorities may use a “range of tools” to control and monitor them.
Turkey’s interior ministry said it would be sending a total of 23 foreigners to their countries in the following days.
An American, seven Germans, an Irish woman, and a Belgian were among those to be deported.
“Countries can’t just revoke the citizenship of such ex-terrorists and expect Turkey to take care of them; this is unacceptable to us and it’s also irresponsible,” interior minister Süleyman Soylu told reporters last week. “Turkey is not a hotel for foreign terrorists.”
One suspected Isis fighter, a US citizen of Jordanian origins, has been stuck on the border between Turkey and Greece, which has refused to allow him entry. He was deported to the US on Thursday.
“Necessary procedures have been launched to send the foreign terrorist fighter stuck in the buffer zone to the US, upon a US commitment,” Turkey’s state-funded Anadolu news agency reported.
The wave of deportations comes after a White House meeting on Wednesday between Turkish president Recep Tayyip Erdogan and Mr Trump, who has hectored European leaders for failing to take back nationals who joined Isis in recent years.
Lisa Smith, an Irish woman who allegedly joined Isis, and her two-year-old daughter, are set to be deported to Ireland.
Turkey says it has captured about 1,200 foreign nationals suspected of having links to Isis.
Both Turkey and the US have complained about Europe’s reluctance to take back their nationals.
“We will continue sending them, so if they take them or do not take them doesn’t really concern us,” Mr Erdogan said on Tuesday before leaving for the US.
European officials have insisted that Isis suspects should be tried in Syria and Iraq.