The escape was discovered when prison officers found two mannequins in the prisoners` beds on Monday.

One of those who escaped is serving a "very long sentence", the BBC`s home affairs correspondent Danny Shaw said.

It is understood the inmates, aged 28 and 31, used diamond-tipped cutting equipment to break through cell bars before they scaled the perimeter wall.

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The police were called at 11:44 GMT.

A prison spokesperson said: "Public protection is our top priority and we take escapes from custody extremely seriously.

"We are working closely with the police and are urgently investigating the matter."

The escaped prisoners were on G wing, the same wing where 21-year-old prisoner Jamal Mahmoud was fatally stabbed last month.

Basana Kimbembi, 34, has been charged with his murder.

Following the attack, about half of the 200 prison officers passed a vote of no confidence in Pentonville governor Kevin Reilly.

The officers claim they cannot stop drugs and weapons being thrown over prison walls.

Camilla Poulton, chair of the Pentonville Prison Independent Monitoring Board, said: "Clearly this is a regrettable incident.

"As we reported in the summer to the Secretary of State for Justice, HMP Pentonville will remain a soft target for contraband and other security breaches as long as its dilapidated windows are in place, notwithstanding the efforts of management and staff."

She added a member of the monitoring board was at the prison on Monday and that it would closely follow the prison`s response to the escape.

The last prisoner to escape from Pentonville was convicted murderer John Massey in 2012.

He sneaked onto a roof after a gym session and then climbed the prison`s 25ft (8m) outer perimeter wall using a rope made from netting.

He was found two days later.

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