Figures from the National Offender Management Service (Noms) show that 90 absconders who have fled prisons in the last decade were still at large at the end of the last month.
Another 79 have not returned after being granted temporary release since 2004.
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Ms Leadsom has received the backing of Ian Duncan Smith, the former work and pensions secretary.
The former shadow work and pensions secretary is considered a more viable candidate than Angela Eagle, a Labour source has told ITV News.
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