Boris Johnson has been accused of presiding over a “chaotic free-for-all” on workers rights under new plans to allow British courts to overturn rulings by the European Court of Justice after Brexit.

Downing Street confirmed that British judges would be handed powers to challenge ECJ rulings through a new clause in Mr Johnson’s Brexit legislation, which MPs will vote on before Christmas.

The move would see the prime minister rip up Theresa May’s commitment to transfer all EU law onto the domestic statute books, which meant it could only be overturned by the Supreme Court or the High Court of Justiciary in Scotland.

Under new plans, UK judges in lower courts would be given powers to overturn ECJ rulings, prompting fears over protections on workers rights and regulations enshrined in European law.

Emboldened by his 80-strong majority, Mr Johnson will bring his Brexit deal to the Commons on Friday for a crucial vote to allow it to clear its first parliamentary hurdle.

“The bill will ensure that the Supreme Court is not the only institution able to consider retaining ECJ rulings,” the prime minister’s official spokesman told a Westminster briefing.

“This is an important change which will ensure that we do not face a legal bottleneck and inadvertently stay bound by EU rulings for many years.

“We will take back control of our laws and disentangle ourselves from the EU’s legal order just as was promised to the British people.”

Asked whether rights will be rolled back, Mr Johnson’s spokesperson said: ​“These will be matters for the British courts as was promised to the British people.

“In relation to workers’ rights, there is a commitment by the government in its manifesto, which will be honoured in full, to ensure that we protect and enhance workers’ rights – and that will be done in UK law.”

Trade unions warned that the move could allow exploitative bosses to try to challenge protections for low paid workers, which have been built up over several decades.

Dr Jason Moyer-Lee​, the general secretary of IWGB, which represents gig economy workers, said: “This government has wasted no time in showing its true colours.

“Low-paid workers have benefited from the EU court’s more generous interpretation of employment rights, in particular, the right to paid holidays.

“Today’s announcement will lead to a chaotic free-for-all with exploitative employers trying to re-litigate every positive development in workers’ rights from the past several decades. The bosses have a true ally in this prime minister.”

Frances O’Grady, the general secretary of the TUC, said: “The prime minister said he will protect all existing rights for workers. The TUC is clear that has to include important case law on workers’ rights.

“No more excuses – no one voted to lose their rights at work after Brexit.”

Mr Johnson plans to fast-track the withdrawal agreement bill through parliament within weeks to allow him to keep his promise to “Get Brexit Done” by 31 January.