How difficult is it for a police force to change? A review of the Metropolitan police by Baroness Louise Casey says racism, misogyny, and homophobia are at the heart of the force. The Met's commissioner Sir Mark Rowley admits 'we have let Londoners down'. Everyone agrees change must happen – but where to start?

Margaret Heffernan meets experts on police reform and former senior officers to explore the organisational challenge that faces any force which wants to transform itself and re-establish public trust. She hears from those involved in establishing the Police Service of Northern Ireland, following the Good Friday Agreement. What were the political and organisational challenges that faced the PSNI in terms of recruitment from two different communities? What lessons might that process offer to the transformation that is needed across other forces? And how would organisational psychologists suggest tackling and turning round long established cultures?

Presenter: Margaret Heffernan Producer: Philip Reevell Editor: Clare Fordham

Greta Gerwig and critics discuss Barbie and Oppenheimer