The government’s Brexit strategy is in danger of driving the UK down a “very slippery slope” towards “dictatorship” or “tyranny”, according to a former president of the supreme court. Addressing an online meeting of lawyers, Lord Neuberger on Wednesday evening condemned the internal market bill, which enables the government to breach international law and exempts some of its powers from legal challenge. “Once you deprive people of the right to go to court to challenge the government, you are in a dictatorship, you are in a tyranny,” Neuberger told the webinar. “The right of litigants to go to court to protect their rights and ensure that the government complies with its legal obligation is fundamental to any system … You could be going down a very slippery slope.” His comments came as the Scottish parliament at Holyrood voted by 90 votes to 28 against granting legislative consent to the Westminster bill. The Scottish National party, Labour, Green and Liberal Democrat MSPs united to oppose the legislation; only Conservative MSPs supported it. The vote will not prevent Boris Johnson’s government at Westminster from pushing through the internal market bill, but the Scottish constitution secretary, Mike Russell, said the Scottish parliament had “explicitly” and comprehensively rejected it. The hastily assembled online panel opposing the bill, organised by the International Bar Association, included Lord Neuberger, the former home secretary and Conservative party leader Michael Howard, the former attorney general Dominic Grieve QC, the SNP justice spokesperson Joanna Cherry QC, Helena Kennedy QC and Jessica Simor QC. All hoped the internal market bill would be defeated in parliament – overturned and fatally delayed by the House of Lords – rather than being challenged in the courts. Cherry said she feared it would end up in the courts and the Scottish government might itself have to initiate legal proceedings against the Westminster government. Neuberger warned that any hearing would “put the judges in a position where they are on a collision course with the government or are seen to be craven … [But] you have to sort out problems in court, if you don’t you have a civil war.” Lord Howard told the online rally, which attracted more than a thousand participants, that he was “opposed to the clauses in the bill which breach international law”. “I’m opposed because I think governments ought to keep their word and uphold treaties,” he said. “I hope this bill is defeated in parliament not in the courts.” Grieve said not only did the bill breach international law, it contained an “ouster clause which goes to the heart of parliamentary democracy”, preventing the government being challenged over its actions. Rather than Brexit being “an assertion of sovereignty,” Grieve added, “it constitutes its undermining”.