Hundreds of people who have protested outside UK courts in recent months are urging the new solicitor general to stop legal action against activists reminding juries of their right not to convict. A letter being delivered on Monday to the Ministry of Justice criticises Robert Courts, who started his role just before Christmas, for serving papers on 68-year-old Trudi Warner, beginning the formal process of having her prosecuted with contempt of court. Warner was charged last year for holding a sign outside Inner London crown court spelling out the right of a jury to acquit a defendant based on their conscience. The statement referred to a famous marble plaque in the Old Bailey celebrating the independence of jurors in the “Bushel’s case” of 1670, where a jury refused a judge’s direction to find defendants guilty. Warner was protesting over restrictions in climate activist cases, imposed by Judge Reid, which prevented defendants from mentioning climate change, insulation or fuel poverty in front of a jury. The prosecutions have inspired a succession of escalating protests across the UK under the banner Defend Our Juries. In December, more than 500 people sat outside courts all over the country holding similar signs while administrative staff, lawyers, judges, jury members and the public queued to get through security. Protesters were also present outside the trial of Extinction Rebellion co-founder Gail Bradbrook, who was given a 15-month suspended sentence in December for criminal damage. Several sign-holding protesters, including Laura Kaarina Korte and Indigo Rumbelow, have been arrested and interviewed but no other charges have been levied. Most of those involved have not faced any consequences for their actions. The 300 signatories of the latest letter describe the decision to prosecute Warner as an attack on free speech and democracy. “In response to such violations of constitutional principle … a broad alliance from civil society has emerged, consisting of members of the public, lawyers, academics and other professionals,” they say. Dr Clive Dolphin, speaking on behalf of Defend Our Juries, said jurors are some of the few people in the criminal justice system who can apply their conscience, but they can only do that if they have all the facts. He added that the issue went far beyond climate change. “There are all sorts of places where it’s important to understand someone’s motivation. So once you pervert the criminal justice system to allow you to crack down on protesters for the environment … that affects a whole swathe of criminal justice procedures.” Civil liberty campaigners have said Warner’s prosecution is part of a growing government crackdown on the right to protest, and last month the UN special rapporteur Michel Forst condemned the UK’s approach. Activists have also expressed concern about the inconsistency with which protest cases are being tried. The signatories to the new letter write that, if the solicitor general stands by his decision to prosecute Warner, then he should do the same to everyone who held similar signs. Courts was appointed solicitor general in December, replacing Michael Tomlinson. He welcomed the UK setting a net zero target in 2019 but has voted against numerous other measures to tackle climate breakdown and is now fighting the development of a large solar farm in his constituency. The government has continued to try to restrict what protesters can say in court. The attorney general recently asked the court of appeal to review whether climate protesters can make the argument of “consent” in court, a hearing on which is being held later this month. This is understood to be a direct reference to a November trial in which a jury cleared nine women of criminal damage for breaking the windows of HSBC’s headquarters in London. The judge allowed them to argue that they truly believed HSBC’s shareholders would have agreed to their actions if they had known the scale of the climate crisis and the bank’s contribution to it. Similar arguments have been used by Palestine Action activists on trial for targeting Israel’s largest private weapons company. The latest move by the attorney general echoes a court of appeal ruling that restricted criminal damage defences after the acquittal of four people who toppled a statue of the slave trader Edward Colston in Bristol.