John Massey is understood to have hid in the prison's gym yesterday until he could sneak on to the roof and escape over the wall without being stopped.
It is thought his makeshift rope was made from bedsheets.
Pentonville was described by prison inspectors as one of Britain's most challenging jails to run last year, but the inspection also found "no obvious problems with physical security".
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Former Chancellor Lord Geoffrey Howe was Margaret Thatcher's longest-serving Cabinet minister, also taking on the role of Foreign Secretary.
Lord Geoffrey Howe is known by many for his resignation speech which was seen as the catalyst which destroyed Margaret Thatcher.
This week daytime temperatures reached 19C. Next week we are expecting 13C by day and close to freezing at night.