Clarke has been vocal in his retirement in campaigning for tougher legislation on terrorism. This has including extended detention before charge for terrorist suspects, giving examples of where it has sometimes proven necessary to make arrests at an early stage in inquiries to protect the public sufficiently. In April 2014, he was appointed to lead an investigation into
Operation Trojan Horse, an alleged plot by
Islamists to take over schools in Birmingham. Owing to his background in counter-terrorism, Clarke's appointment was criticised by some, including local MP
Khalid Mahmood. In February 2016, he was appointed
HM Chief Inspector of Prisons in a written statement to Parliament by Michael Gove. His appointment ended in October 2020. == Honours ==