Ministers have been warned by a former head of the judiciary that plans to let the UK ignore rulings from the European court of human rights (ECHR) on small boat crossings could be defeated in the House of Lords. John Thomas, who was lord chief justice of England and Wales from 2013 to 2017, said the move would probably amount to a “symbolic breach of the rule of law”. He criticised the government for caving in to a group of hard-right Tory MPs who had threatened to launch a rebellion during the final parliamentary stages of the illegal migration bill. About 30 backbench rebels have been pushing Rishi Sunak to harden the legislation so ministers can ignore interim rulings. One of the Strasbourg court’s rule 39 injunctions blocked the government’s first attempt to deport asylum seekers to Rwanda last year. These interim measures are typically used to suspend an expulsion or extradition, often in the case of asylum seekers who fear persecution if they are returned to their home country. Lord Thomas expressed concern that the government would table amendments to the illegal migration bill in advance of the crunch vote next week. “I think it is a very serious step for the government to be contemplating putting into force,” he told BBC Radio 4’s Today programme. MPs will consider the remaining stages of the illegal migration bill in the Commons on Wednesday 26 April, according to the Commons leader, Penny Mordaunt. The chamber will discuss and vote on proposed amendments to the bill before it is sent to the House of Lords for further scrutiny. Thomas said: “Many people would say having the power to ignore a court order is something [that], unless the circumstances were quite extraordinary, [that] this is a step a government should never take because it is symbolic of a breach of the rule of law.” Days of wrangling between the group of prospective rebels – led by Danny Kruger – and Sunak and the immigration minister, Robert Jenrick, ended on Wednesday. The prime minister met members of the Common Sense Group of Tory MPs earlier this week and reassured them he had “skin in the game, too” having promised to “stop the boats”. There may also be a sop to another group of MPs who want the government to commit to establishing safe and legal routes available to people to claim asylum, with an annual cap on numbers. Though some Tory MPs are pushing for the UK to leave the ECHR, they have conducted a “tactical retreat” from pushing for the government to do so before the next election. Instead they are focusing on getting the commitment inserted into the party’s next manifesto. Removing the UK altogether from the ECHR, the rights of which were incorporated into UK law in 1998 with the Human Rights Act, is viewed as problematic as the court was an integral part of the Good Friday agreement that brought peace to Northern Ireland. Labour suggested the prime minister was forced to “cave in” because he was “weak”. The shadow Commons leader, Thangam Debbonaire, told MPs: “Is this because the prime minister couldn’t even get his own MPs to line up with him? Because it does look that way; that we are here again with a weak prime minister forced to cave in to appease a small minority of rightwing backbenchers. What a mess.”