Susan Hall, the Tory candidate for London mayor, has joined a Facebook group which contains Islamophobic hate speech and abusive comments about her opponent Sadiq Khan, the day after an exposé about its contents. Khan told the Guardian these revelations “could have a direct impact on not just my safety but the safety of my family and staff”. A joint investigation by the Observer and Unearthed at the weekend profiled a network of Facebook groups focused on ultra-low emission zones that are operated by Conservative party staff and activists and which contained Islamophobic hate speech, conspiracy theories and abuse. Some of the groups included celebrations of vandalism and comments expressing disbelief that Khan had not been “taken out”. Hall was already a member of six of the groups. On Monday, the day after the revelation, her official Facebook page joined a seventh group called “Bexley say no to Ulez expansion”. The contents of the group include: A YouTube video alleging that “Islamists” were “taking over Britain”. Abuse towards Khan, including a post that read: “Seriously can’t believe Khan hasn’t been taken out yet … if dark forces can take out Princess Diana I’m sure they can take out this money grabbing little parasite”. Examples of vandalism: one user shared a photo of an enforcement van with its tyres slashed, noting “two flat tyres and sprayed camera”. Another user responded: “Well done to whoever that was”. Numerous Islamophobic comments, including one commenter calling Khan a “terrorist sympathiser”, and another saying that the London mayor “will see a big upsurge in public feelings and possibly major riots, mosques burnt down and innocent Muslims unable to walk the streets”. The investigation identified 36 groups that appear to be separate grassroots movements opposing the expansion of ultra-low emission zone (Ulez) schemes to reduce air pollution. They do not say they were set up by the Conservatives as part of a coordinated political campaign, but it has been found they were set up by Conservative staff and activists. There is no suggestion the racist posts or those encouraging vandalism were made, or engaged with, by Conservative politicians or staff. Khan told the Guardian: “This latest revelation is absolutely jaw dropping. This could have a direct impact on not just my safety but the safety of my family and staff. No one should be inciting violence … There is no doubt in my mind that if she [Hall] won, this Tory would be the most dangerous and divisive mayor London has ever had. “The election on Thursday will be close between Labour and the Tories. The choice is clear: a fairer, safer, greener London with Labour or the Tory candidate who will divide our communities and take London backwards.” The Labour party has reported the groups to the police, Khan added. The Labour MP for Brent Central, Dawn Butler, has also raised the matter in the House of Commons and written to the Metropolitan police high commissioner to urge action. In her letter, she wrote: “I believe that many of these posts constitute racially or religiously aggravated offences … I find it shocking that these potential crimes have been committed in Facebook groups where several prominent Conservative politicians are active members. Conservative candidate for mayor of London, Susan Hall, has yet to explain why she is a member of groups peddling hate in this way, and Londoners will be concerned she appears to be condoning this behaviour.” Senior Tories have made posts in some of the groups. Hall is a member of seven groups and has posted in two. A Tory activist posted a meme calling Khan an “arse” alongside laughing emojis in one of the groups. Ami McCarthy, a political campaigner at Greenpeace UK, said: “Any respectable politician would have issued an apology and left these Facebook groups as soon as the racism, Islamophobia and posts inciting criminal damage were exposed. But not Susan Hall – she’s just brazenly doubled down and joined another hotbed of hateful and derogatory posts. “Bolstering her support for the anti-Ulez brigade appears a last-ditch attempt by the Conservative mayoral candidate to boost her ratings. But the majority of Londoners want a mayor that will strive to tackle the climate crisis, reduce harmful air pollution in the capital and doesn’t associate with people who traffic in racism and conspiracy theories. So her strategy may well be doomed.” Hall and the London Conservatives have been contacted for comment. A spokesperson distanced CCHQ from the racist and abusive comments when details of the groups were first revealed, saying the party “unequivocally condemns all discriminatory language, and never encourages nor condones vandalism or criminal activity”.