Katie Razzall: A seismic moment that shows rift at top of BBC

Tim Davie resigns as BBC Director General & CEO of BBC News simultaneously, citing intense pressures of the role & recent controversies. Deborah Turness also resigns on principle amid ongoing Panorama controversy. BBC faces institutional bias accusations & criticism for handling of Trump speech edit. Internal rift emerges between BBC Board & news division, as organization grapples with leadership changes amidst challenges.