Theresa May has been accused of offering “meaningless empty rhetoric” on workers’ rights to win support for her Brexit deal, while quietly eroding vital protections in a no-deal scenario.

The prime minister is expected to formally announce a package of measures on workers’ rights next week, as she scrambles to woo Labour MPs to support her Brexit plan.

But without much fanfare, ministers have amended key employment laws in the event of a no-deal Brexit, including regulations that enshrine the rights of workers if their company is taken over and the existence of union-style works councils for workers in multinational firms.

Labour and union leaders said these legal tweaks – known as statutory instruments (SIs) – actually amount to significant changes to the law if Britain leaves the European Union without a deal, and could leave British workers at a disadvantage.

Shadow business secretary Rebecca Long-Bailey told The Independent: “The prime minister has waxed lyrical about protecting workers’ hardwon rights after we leave the EU.

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“However, as these employment statutory instruments show, it was nothing but meaningless empty rhetoric.

“After eight years of crippling austerity, workers are forced to work in increasingly precarious conditions. By rushing these changes to legislation, they are leaving British workers at a severe disadvantage compared to their EU colleagues.”

The SIs have now been approved in the Commons, despite concerns raised by MPs that the loss of European Works Councils would prevent British workers from large multinational companies having a voice in line with European colleagues.

Shadow minister Justin Madders told MPs in the debate that the change “clearly constitutes a loss of valuable workers’ rights in contravention of the PM’s promise to maintain existing workers’ rights at current levels”.

Business minister Kelly Tolhurst was also warned that the changes risked “watering down” Tupe protections, which protect workers when a business is taken over by a new employer.

Mr Madders said ministers could not “nod through” changes when thousands of employees could be affected, as it will apply to public sector services, PFI and outsourcing contracts.

But Ms Tolhurst argued the SIs were only “minor changes to language” and would protect workers from uncertainty if Britain crashes out of the EU without a deal.

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The Trades Union Congress said the move would would make it easier for UK workers to fall behind their European counterparts.

A spokesperson said: “The prime minister has promised that workers’ rights will be protected and enhanced after Brexit. But these regulations show that, despite her warm words, her government’s actions are taking us in a different direction.

“The regulations would erode valuable rights relating to European Works Councils. And they would remove powers that allow ministers to keep UK law in line with EU law. This would make it easier for UK workers’ rights to fall behind those in the rest of Europe.

“The prime minister is eager to cast herself as a champion of workers’ rights. But the reality is that her Brexit deal puts rights at risk.”

The new government legislation comes as the prime minister was expected to make a last-ditch attempt to win over Labour politicians in Leave-voting areas with a package of measures on workers rights ahead of the meaningful vote on 12 March.

Electronic balloting for trade union members is another issue reportedly being considered by Downing Street, allowing union leaders to organise strike action more efficiently.

Ms May also confirmed at prime minister’s questions on Wednesday that there would be a fund to “ensure our towns can grow and prosper” after widespread speculation she was planning to offer cash to MPs in former industrial heartlands.

A government spokesperson said: “This legislation provides certainty and legal clarity to employers and workers in the event of a no-deal scenario. As we leave the EU, we will protect workers’ rights and continue to enhance them.