After three years running Brixton prison, Paul McDowell is now at the heart of a debate about whether charities should run prisons.
Last year, McDowell ended a 20-year prison service career when he relinquished the governor's job at the south London prison to become chief executive of crime-reduction charity Nacro.
He accepted the post four days before he was due to become governor of Wandsworth prison. "They had already put my name on the door," he says.
When he joined Nacro it had just bid with private company G4S to run five prisons. Some other charities, including Turning Point and Catch 22, also worked on bids with private companies to run prisons, provoking fierce debate on whether charities could or should get involved in locking people up. Kevin Curley, chief executive of local infrastructure group Navca, set up a Facebook group opposing it and asked the Charity Commission to investigate whether running prisons was a charitable purpose. McDowell says opposition is based on ideology rather than what is actually happening.
"If G4S is successful, the role Nacro will play will be as a subcontractor and deliverer of resettlement services," he says.
"We work in 30 prisons providing exactly the same services."
He says it would be "morally wrong" for charities to abandon service users by refusing to collaborate with private companies, but insists Nacro has no intention of actually running prisons.
"That would mean stepping outside our area of expertise and roles we have set ourselves," he says. "I don't know of a charity whose principles fit with running prisons."
McDowell says that after two decades of "hard slog" in prisons, his first voluntary sector role allows him new freedoms.
"I'm somebody who can claim to have been stuck on the front line for two decades," he says. "I understand criminal justice and offenders."
McDowell says Nacro will continue to focus on resettlement, but will lobby harder, beginning with a conference this week when he will call on political parties to join a cross-party round-table debate on attitudes to imprisonment.
During McDowell's career in the prison service, the number of inmates doubled to 80,000, and he wants to campaign for fewer people to be locked up, even if this means incurring the wrath of the Daily Mail. "If I'm not willing to do it, why should I expect politicians to?" he asks.
It's a daunting prospect, but after working with some of south London's most hardened criminals, he isn't fazed.