‘We’ve made this programme for Black parents,’ Mike Phillips said, introducing ‘Black Teachers’ on BBC2 in 1973. ‘We’ve got no intention of wasting our time on proving things that we all know.’ ‘Black Teachers’ was an episode of Open Door, a product of the BBC’s Community Programme Unit, founded a year earlier to profile groups and causes that had been ‘unheard or neglected’ by the media establishment. Its archive has been inaccessible for decades, but People Make Television, an exhibition at Raven Row in Spitalfields until 25 March, aims to change that, presenting a tightly curated – but still vast – selection of the material produced by the unit and its offshoots.