When one of the world's richest men bought Twitter, almost everything there changed. Thousands of staff were sacked and users previously banned for breaking Twitter's rules were reinstated. Panorama investigates how Elon Musk's ownership is transforming one of the world's most influential social media platforms. Reporter Marianna Spring speaks to current and former insiders in San Francisco and the UK and reveals how hate and misogyny are thriving under the new owner.