On Sunday, Russia’s former deputy prime minister and head of the Roscomos Space Agency warned Warsaw it risked “losing everything” if it continued a territorial dispute over the Black Sea port of Kaliningrad. 

Dmitry Rogozin issued the threat after a Polish general called for Kaliningrad, which was captured by Soviet Forces in World War Two but lies between Lithuania and Poland, to be returned to Warsaw.

“As you can see, the Russian Federation, following the end of World War II received only the small Kaliningrad region,” Mr Rogozin wrote in a Tweet beside a map of what he said showed the expanded post-war territories of Poland, Latvia, the Czech Republic and Ukraine.

“It is definitely not in their interests to stir up the territorial questions and interests of their neighbour. Afterall, you can lose everything,” he said.

Poland’s Territorial Defence Force, which numbers around 30,000 soldiers, has seen a seven-fold increase in interest from prospective recruits since the war began.

The volunteer reserve force was established in 2016 in response to fears of Russian expansionism and the invasion of the Donbas region in eastern Ukraine.

Poland shares a border not only with Ukraine, but also with Belarus and the Russian enclave of Kaliningrad.

The Polish military has an overall strength of 120,000 personnel, from the army, navy and air force to special forces and the Territorial Defence Force.

The government has ambitious plans to more than double that number to 250,000 and aims to become the strongest military power in central Europe.

The military is equipped with a mixture of Soviet-era equipment and more modern Western weapons systems, including the latest combat aircraft, frigates, helicopters and unmanned aerial vehicles.

There has been “enormous interest” in joining up compared to prior to the war, a spokesman for the TDF said.