BBC has the details…
A British man has been captured by Russian forces while fighting for Ukraine, according to reports.
In a video circulating online, a man dressed in military clothing identifies himself as James Scott Rhys Anderson, 22, and says he formerly served in the British Army.
Russian state news agency Tass quotes a military source saying that what they call a “UK mercenary” had been “taken prisoner in the Kursk area” of Russia, part of which Ukraine has held since launching a surprise offensive in August.
…
Scott Anderson, Mr Anderson’s father, said he had begged his son not to go to Ukraine.
“He wanted to go out there because he thought he was doing what was right,” Mr Anderson told the Daily Mail.
I am not sure how Russia will treat an armed incursion on its territory by a foreign national. He could be exchanged by some Russian agents held by the British eventually in the better case. Otherwise he could also spend time in Russian jail.
Insomniac Resurrected 