A secret Islamic State camp in Syria is training Western jihadists to smuggle themselves into Europe and launch attacks on British soil, a captured fighter has claimed, predicting “more suicide attacks in Europe”.

The shady unit, behind the deadly attacks in Paris and Brussels, has trained fighters from countries including Germany, France, Belgium, and Britain, and is now focused on striking the UK.

“They are in contact with sleeper cells there,” said the fighter, who has been with Islamic State for two and a half years and claims more than 50 terrorists have graduated the elite unit.

British fighters receive bomb construction tutoring, religious ideology training, and go through harsh physical endurance trials. Crucially, all recruits must be willing to lay down their lives for Islamic State, the militant said.

“It takes seven months to be trained in al-Kharsa brigade,” he added, in an interview that was conducted by The Sunday Times in front of his Kurdish captors.

“It is very hard. Every European who crosses the border to Syria, they are offered [the opportunity] to join. If 20 start the training, only five finish it. Then after that they go back to Europe and attack.”

Despite territorial losses suffered by the group, he said the division is still operational. In fact, as Islamic State crumbles in Iraq and Syria, the unit may become even more deadly, as some fear a wave of battle-hardened terrorists will seek to return to Europe.

“They will make more suicide attacks in Europe because the coalition is bombing them a lot,” he said. “They also want to carry out attacks in Lebanon.”

Attacks in the West and the training at the al-Kharsa camp are organised by Islamic State’s external operations wing, previously run by the group’s feared second in command, Abu Muhammad al-Adnani, until he was killed in 2016.

Al-Adnani oversaw many attacks, included Dhaka, Bangladesh, Paris, and Brussels. In the latter two incidences, the terrorists posed as ‘refugees’ to travel to Europe, including Belgian-Moroccan ringleader Abdelhamid Abaaoud.

“The attacks that happened in Paris and Brussels, the attackers were trained by them and left from Syria to Europe,” said the fighter. “Sometimes there are foreigners who come to Syria and have training for specific missions. Then they do the attacks alone.

“Others are sleeper cells in Europe who want to join Daesh [Islamic State] here, but can’t. They stay in their countries and contact [Islamic State]. Then they talk, and when they are ready they do the bombings.”

Gilles de Kerchove, the European Union Counterterrorism Coordinator, said that one-third of an estimated 5,000 European jihadists who were trained in Syria and Iraq have returned to their home countries, many undetected by authorities.

He estimated that there were some 2,000 to 2,500 European “foreign terrorist fighters” still in Syria and Iraq, Reuters reports.

“There are largely two categories of returnees: those in the majority who will drift back and those who will be sent back on specific missions, which are of most concern,” he added.