Violent prisoners have been using illicit mobile phones to post naked pictures on social media as they brag about their cushy life behind bars .

The antics of the brazen lags – including one freed killer returned to jail for armed robbery and assault – expose a shocking lack of prison security .

Nude photos of Michael Roberts and his fellow inmates have been posted online using illegally held mobile phones.Knife robber Roberts shared the snaps on Instagram and Facebook, boasting of an easy life in high-security Saughton Prison, Edinburgh, the Daily Record reports .

Roberts, 22, who gleefully mocks prison bosses in his posts, also uploaded a video of his killer pal John Reid punching another inmate.

His posts were made under the name Mikey 00tsoon on Facebook and MikeyRoberts30 on Instagram.

One added on Monday showed him and fellow inmate Lee Ridgway with the comment: “Me and ma brother chilling.”

One video posted online shows a prisoner standing in a cell waiting to be punched in the face on camera by another inmate, who is wearing a black hood over his head to hide his identity.

The hooded con is understood to be Reid – known as the one-punch killer.

Reid was just 16 when he killed Simon San, 40, with a single punch outside the San family’s takeaway restaurant in Lochend, Edinburgh, in 2010.