Bradley Manning, the alleged source of the Wikileaks US embassy cables, is technically a British citizen, according to claims by high profile human rights organisations and lawyers.

Manning, who worked as a soldier in the US, is charged there with mishandling and transferring classified information. He is currently held in a maximum security jail in Virginia.

He once wrote in an online chat that he would go into work “with music on a CD-RW labelled with something like Lady Gaga... erase the music... then write a compressed split file” containing the downloaded documents. He said he would even lip-synch the songs as he downloaded the classified documents.

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But while he was born in the US and grew up there, Manning is technically a British citizen by descent from his Welsh mother, and has dual nationality with the US. This is according to the British Nationality Act of 1981, observers from human rights organisations and immigration law firms pointed out.

As the conversation around his nationality spread across Twitter, Amnesty International last night called on the UK government to immediately intervene on Manning’s behalf.

Branding his current US detention as “harsh and punitive”, the human rights organisation called for the government to ensure Manning’s treatment meets international standards.

“His Welsh parentage means the UK government should demand his ‘maximum custody’ status does not impair his ability to defend himself, and we would also like to see Foreign Office officials visiting him just as they would any other British person detained overseas and potentially facing trial on very serious charges.”

Manning is in solitary confinement 23 hours a day, and shackled by his feet and hands when he has visitors. He was recently put on suicide watch.