British workers could lose many of their employment rights after Brexit unless the Government draws up new laws to protect them, a senior Labour MP has warned.
Prominent Brexiteers rubbished claims made during the referendum campaign that leaving the EU would result in a bonfire of workers' rights.
But former shadow business secretary Chuka Umunna has commissioned research by the House of Commons Library highlighting the EU laws that enshrine employment rights.
Mr Umunna, chairman of Vote Leave Watch, which scrutinises claims made by Brexit campaigners, has written to the Prime Minister warning her that a failure to protect these rights would amount to "a betrayal of British workers".
The letter states: "You have said repeatedly that 'Brexit means Brexit'. But you must now begin to set out what this means.
"You owe it to the working people of Britain to make clear that the pledges made by your Cabinet colleagues to retain EU legislation on workers' rights will be delivered.
"Anything else will be a betrayal of British workers, whether they voted to leave the EU or to remain a member. Do the right thing by the working people of Britain, and commit unequivocally to protecting the rights on which dignity at work depends."
He is calling on the PM to confirm the Government will ensure all employment rights currently dependent on EU law remain in place post-Brexit by passing fresh legislation if necessary.
He is also urging a full audit of all instances where decisions of the European Court of Justice have delivered rights for British workers, and a commitment to ensure judgments are retained post-Brexit.
And he wants the PM to make clear Britain's full support for the Equality Act 2010.
John Hannett, patron of Vote Leave Watch and general secretary of the USDAW trade union, said: "Being part of the EU has protected British workers, my members among them, from discrimination, unscrupulous bosses, and the worst excesses of Tory governments.
"The Prime Minister came to office talking a good game about standing up for working people. She now has to walk the walk - and the first part of that should be guaranteeing that every single right for workers delivered by the European Union will stay in place.
"Anything less would be a betrayal of British workers, especially given the promises that were made on employment rights by members of the Vote Leave campaign. Every worker and trade unionist in Britain urgently needs clarity on this vital issue."
A Downing Street spokesman said: "Britain voted decisively to leave the EU - and this Government will deliver the people's verdict. In every step we will work to ensure the best possible outcome for the British people.
"We don't need to be part of the EU to have strong protections for workers' rights."