His unit has recently been defending the besieged city of Mariupol, which has been heavily bombarded by Russia.

His mother Ang Wood said her son told her he had no choice.

"He called me and said they have no weapons left to fight," she said.

Ms Wood said her son - a former care worker who previously fought with Kurdish armed units in Syria against so-called Islamic State - "sounded okay", but called for the UK government to provide more support to Ukraine.

"Boris [Johnson] needs to take [Vladimir] Putin down," she added.

Brennan Philips, a friend of Mr Aslin who also spoke to him by phone, said he sounded "strong and in good spirits".

"He called me and said 'we have no food, no supplies, no ammo, we're completely surrounded, we have to surrender'," he said.

"Aiden was very well aware of what was going on, very calm.

"They can't get out, they can't fight back so they had no choice.

"I'm sure if they had a bullet left they would have shot it."