A secretive Isis division has been teaching UK fighters to launch attacks on British soil, according to a fighter reportedly captured by Kurdish troops in Syria.

The militant described how the unit trained those involved in the Paris and Brussels attacks. He also revealed the ways in which the new recruits were initiated into the al-Kharsha brigade in Syria, according to a Sunday Times report.

British fighters are said to take part in a rigorous training regime before flying home to carry out attacks.

“It takes seven months to be trained in al-Kharsa brigade,” the fighter said while he was interviewed 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.”

Giving detailed information, the Isis fighter said that about 50 people went through the programme from countries including the UK, Belgium, France and Germany.

The instruction given at the Syrian camp involved bomb construction, religious ideology according to Isis as well as going through harsh physical endurance trials. All recruits had to be willing to give up their lives for the Isis cause, the militant said.

The unit was under the umbrella of the external operations arm of the so-called Islamic State, the Amniyat Amniyat al-Kharji. It’s believed that the Amniyat is now focusing on working with sleeper cells.

According to the Sunday Times, past fighters included Belgian-born Abdelhamid Abaaoud, who led the Paris attacks in which 130 people were killed. Abaaoud was shot dead in a raid by French police five days after the massacre.

In pictures: Isis' weapons factories Show all 11 1 /11 In pictures: Isis' weapons factories In pictures: Isis' weapons factories A mortar round fin manufactured by Isis in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis rocket components discovered in Gogjali, Mosul, Iraq in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortars discovered near Karamlais, Iraq, in November 2016 CAR In pictures: Isis' weapons factories An Isis rocket launch frame in Qaraqosh, November 2016 Conflict Armament Research In pictures: Isis' weapons factories A memo from Isis' COSQC on quality control at a manufacturing facility in Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Electrically-operated initiators manufactured by Isis in forces Gogjali, Mosul, November 2016 Conflict Armament Research In pictures: Isis' weapons factories Isis mortar tubes at a manufacturing facility in Karamlais, November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis mortar production facility discovered in Gogjali, Mosul, in November 2016 Conflict Armament Research In pictures: Isis' weapons factories An Isis weapons manufacturing facilities near Mosul in November 2016 Conflict Armament Research In pictures: Isis' weapons factories Stocks of French-manufactured Sorbitol, Latvian potassium nitrate and Lebanese sugar at an Isis weapons factory in Iraq Conflict Armament Research In pictures: Isis' weapons factories A destroyed Isis weapons facility in Qaraqosh, Iraq, November 2016 Conflict Armament Research

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

He estimated that there were some 2,000-2,500 European "foreign terrorist fighters" still in Syria and Iraq, according to Reuters.

De Kerchove added: "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."