The UK health minister Maria Caulfield is facing calls to refer herself to the ministerial ethics adviser for pushing false claims linked to a recognised conspiracy theory. The Lewes MP defended leaflets in which she said her local council was planning to restrict people’s freedom to drive as part of the establishment of a “15-minute city”. That came days before the leader of the Commons warned that spreading such conspiracy theories threatened the health of British democracy. Daisy Cooper, the deputy leader of the Liberal Democrats, one of the main parties on the council in question, said: “Maria Caulfield should apologise to local people and report her leaflet to the ministerial ethics adviser. That would be the honest and decent thing to do.” She called the leaflets “dishonest”, adding: “After years of Conservative sleaze and scandal, the public desperately wants a return to integrity in politics, yet Maria Caulfield is spreading baseless claims. [She] is deliberately misleading the public to try to save her own job. This is a new low for the Conservative party.” Caulfield said the Lib Dems and Greens – the two largest parties on Lewes district council – wanted to “introduce a road toll system, called 15-minute city … where you will have to pay a congestion charge if you travel by car more than 15 mins from your home”. The “15-minute city” is an urban planning concept that focuses on placing local amenities within about a 15-minute walk of people’s homes. It is designed to make urban areas more pleasant places to live. A conspiracy theory has grown up around it that claims it is actually an attempt to restrict people’s freedoms – locking them into areas around their homes and preventing them travelling freely beyond. It was one of several increasingly common conspiracy theories identified in a guide – given to MPs by the leader of the House of Commons, Penny Mordaunt, last week – as being noxious to British democracy. “The proliferation of conspiracy theories across the UK is deeply disturbing. They are deliberate campaigns to spread disinformation and fear. If they go unchallenged we risk the public being conned and their wellbeing potentially damaged. These campaigns are also a threat to the health of our democracy,” said Mordaunt, Caulfield’s Conservative colleague. Caulfield’s leaflets were sent out during campaigning for elections to Lewes district council last year. The health minister defended her claims during an appearance on BBC Politics South-East on 5 May. She said the proposal was included in the council’s draft local plan. That document proposes making amenities more easily accessible as part of a “10- or 20-minute neighbourhood” scheme, but there is no suggestion of charging people for driving further away from their homes – nor has there ever been, the council’s leader, Zoe Nicholson, said. When that was put to her during the BBC appearance, Caulfield said: “Well, that’s what’s in their document.” Pressed on whether she believed road charges were part of the council’s plan, she said: “It talks about 15-minute cities … Part of 15-minute cities is if you go outside of your 15-minute area, you will have to pay a road tax.” Caulfield denied she was propagating a conspiracy theory and cited the example of Oxford, which has introduced a congestion charge scheme, as evidence of her claim. Responding to the assertion that the Oxford scheme does not include a charge for driving more than 15 minutes from home, Caulfield told the BBC: “That is the policy, though … that is the model of 15-minute cities. [The Lewes document] talks about 20-minute communities, which is what that theory is about.” She is not the only senior Tory to have focused on the 15-minute cities issue. Both the prime minister and the transport minister have raised it in recent months. And a backbench Conservative MP told the Commons it was an “international socialist concept” that will “cost our personal freedom”. Documents seen by the Guardian in January showed government ministers had taken the conspiracy theory into account when devising transport policy. The Conservative party declined to answer when asked if it accepted that Caulfield’s claim the local council planned to charge motorists was incorrect, or if it recognised the distinction between the 15-minute city idea and the conspiracy theory. A spokesperson said: “This is nothing more than a pathetic attempt from the Liberal Democrats to distract from their war on motorists.” Caulfield and the Department for Health and Social Care have not responded to a request for comment.