A British man who joined the lines of the PKK terrorist organization's Syrian affiliate Democratic Union Party's (PYD) and People's Protection Units (YPG) militia, a terrorist group Turkey is now fighting in northwestern Syria, will be prosecuted under Britain's anti-terrorism law, U.K. police said Wednesday.

Scotland Yard said former soldier Jim Matthews will be tried on charges of terrorism.

Metropolitan Police said on its website: "A U.K. national [referring to Matthews] is due to appear at Westminster Magistrates' Court on Wednesday, 14 February to be formally charged with attending a place or places in Iraq and Syria where instruction or training was provided for purposes connected to the commission or preparation of terrorism on or before 15 February 2016, under Section 8 of the Terrorism Act 2006."

Matthews appeared on a TV documentary called "The Brits battling ISIS." ISIS is another name for Daesh. In March 2017, a Jim Matthews was a signatory on an "open letter from British YPG fighters on London attacks" posted on a Kurdish news website.

Although the U.K. has listed the PKK as a terrorist organization since 2001, the YPG, despite its links with the PKK, is not on the list. The United States and the European Union also list the PKK as a terrorist organization. However, the YPG has been supported by the United States, under the umbrella group, Syrian Democratic Forces (SDF), under the guise of fighting Daesh in northern Syria. Ankara has long argued that the YPG is a terrorist organization and that "one terrorist organization cannot be eliminated by partnering with another."

The PKK's 30-year terrorist campaign against Turkey has led to the deaths of some 40,000 people.

In order to eliminate the threats posed by the YPG to Turkey's national security, Operation Olive Branch's cross-border offensive was launched by the Turkish Armed Forces (TSK) backing the Free Syrian Army (FSA) on Jan. 20 in northern Syria.

British authorities have not included the YPG on its lists of terrorist groups, but they have warned that Britons who fight alongside the YPG of the possibility they could be prosecuted under the anti-terror law return when they to the country. A London-based think tank, the Henry Jackson Society, published a report last August, "The Forgotten Fighters: The PKK in Syria," detailing the close ties between the PKK and YPG, and reporting on foreigners joining the terrorist group.

The report profiled 60 foreign fighters from 12 countries, saying that around 80 percent of them come from English-speaking countries. It recommended that the British government take measures to prevent Britons from joining the YPG, adding that those who do should be followed closely. The report warned that Britons who join the YPG could lead to a diplomatic crisis with Turkey, a NATO ally, urging British authorities to distance themselves from the group.

The report also recommended that the YPG be added to Britain's list of alternate names of the PKK so the anti-terror law could be applied to activities under this name.

Several Britons have been killed fighting Daesh alongside the YPG terrorist group. Matthews will be the first British national to have joined the YPG under the pretext of fighting Daesh to be later tried under the anti-terror law.