Campaigners have launched a legal challenge to try to prevent billions of pounds of taxpayers’ money being spent on a huge road-building programme, which they say breaches the UK’s legal commitments to tackle the climate crisis and air pollution. Lawyers acting for the Transport Action Network (Tan) have begun legal proceedings against the Department for Transport calling for the road-building scheme, which was confirmed last month by the chancellor, Rishi Sunak, to be suspended. They argue that ministers did not take into account the government’s legally binding commitment to reach net zero emissions by 2050. They also say the government has not considered whether the £27bn programme is in line with its obligations under the Paris climate agreement. The move follows a successful challenge to the proposed third runway at Heathrow. In that case the court ruled that the planned airport expansion was illegal because ministers did not adequately take into account the government’s commitments to tackle the climate crisis. The road-building programme is thought to be the UK’s largest and would lead to thousands of miles of new roads being built across the country in the coming years – with at least 50 projects due to be under way in the next two years. The UK’s road network and its wider transport infrastructure are crucial in the country’s efforts to avoid the worst impacts of the climate crisis. The transport sector is the biggest emitter of greenhouse gases and the only one to have increased its emissions in recent years. Chris Todd, Tan’s director, said it was impossible to take the government seriously on the threat posed by climate change when it is “set to burn billions on the largest ever roads programme”. “This massive roads programme has become like a juggernaut that’s out of control, that no one can stop. We now have no choice but to go to court to prevent an unfolding disaster.” Tan wrote to the secretary of state following the court of appeal’s Heathrow decision in February requesting a pause in the road-building programme to allow time to reconsider its environmental effects. It said it did not receive a response to that letter. Lawyers have sent a pre-action protocol letter that is the official start of legal proceedings. Rowan Smith, from the solicitors Leigh Day, which is pursuing the case on behalf of Tan, said the group was raising “legitimate concerns” at a time when it was widely established that the climate emergency “demands a move away from a continued reliance on fossil fuels towards more sustainable transport”. The government’s climate change adviser has joined calls for ministers to reconsider its road-building plans. Chris Stark, the head of the Committee on Climate Change, said it would be better for the economy and the fight against climate breakdown for the billions of pounds allocated for road-building to be invested in broadband – especially in light of the coronavirus crisis, which has led to many more people working from home. “The government mustn’t be investing in anything likely to increase carbon emissions,” Stark told the BBC. “I expect that video-conferencing will become the new normal and we won’t return to travelling the way we did. I would spend the roads budget on fibre. You would get a huge return to the economy with people having better connections. You would save people’s time and increase their productivity.” His comments echo those of the head of the motoring organisation the AA, who said this month that government money would be better invested in broadband than roads. In response to the legal challenge, a spokesperson for the Department for Transport defended its plans. “The second road investment strategy is consistent with our ambitions to improve air quality and decarbonise transport,” they said. “We have received the letter and will respond formally in due course.’’