To my understanding, it is a crime for a British national to serve in the armed forces of one of our enemies.
If a dual british/russian national were conscripted and forced to fight in the Ukraine war, what crime, if any, would they be committing and what is the potential punishment should they ever return to the UK?
The United Kingdom is not at war with Russia, so the two countries are not enemies in the legal sense.
However, it is an offence under the Foreign Enlistment Act 1870 for any British subject to serve:
in the military or naval service of any foreign state at war with any foreign state at peace with Her Majesty
(From section 4 of the Act.)
This issue was raised with respect to British volunteers who went to fight with the Ukrainian army, as in theory they were breaking the law. Therefore, we can surmise that anyone who left to fight with the Russian army would also be acting illegally.
However, as the linked article mentions, prosecutions under this Act (or its 1819 predecessor) are extremely rare.
To be clear, Australian in this context means a citizen, a resident, a visa holder under the Migration Act, or a person who has placed themselves under the protection of Australia.
The specific offences in s119 of the Criminal Code are:
enter a foreign country with an intention to engage in a hostile activity, unless serving in or with the armed forces of the government of a foreign country
prepare to enter, or for another person to enter, a foreign country with an intention to engage in a hostile activity, unless serving in or with the armed forces of the government of a foreign country
recruit persons to join an organisation engaged in hostile activities, or to serve in or with an armed force in a foreign country.
As you can see, joining a foreign army is not an offence unless that army has been explicitly prescribed by the AFP Minister (in practice, the Attorney General). AFAIK, this hasn’t happened for any nation’s armed forces.
