The mayors of Paris, Mexico City, Stockholm, San Francisco and Rio de Janeiro came to the Vatican this week to discuss human trafficking. But despite London being seen as a key centre in fighting the problem, the mayor of London, Boris Johnson, was not there. A spokeswoman told us he was unable to attend “due to diary constraints”. But she added he is “delighted that the Vatican is highlighting the issues of climate change and modern slavery, and congratulates Pope Francis on his initiatives in this area.” The gathering for the mayors was for a workshop on modern slavery and climate change hosted by the Pontifical Academies of Science and Social Sciences. While the Mayor of London was not present, Kevin Hyland, the UK’s anti-slavery commissioner, who has work