As usual, all the signal is in comments [1, 2, 3]; so-called 'articles' are just fake news composed by people with a conflict of interest and EPO "media partners".
"In the United Kingdom, the Foreign Enlistment Act 1819 and the Foreign Enlistment Act 1870 make it unlawful for British subjects to join the armed forces of any state warring with another state at peace with Britain."