THE SNP will betray workers if the party drops its opposition to extended Sunday trading south of the border, Labour's shadow business secretary has said.

The nationalists had previously said they would vote against the Westminster move to devolve Sunday trading legislation to councils, despite it only applying in England, due to fears it would cause Scottish workers to lose pay perks.

However, the party has apparently softened its stance, welcoming new measures brought in by the UK Government that it said would protect workers from being forced into working on a Sunday.

Angela Eagle, the shadow business secretary, has written to SNP Westminster Angus Robertson calling on him to clarify his stance. The nationalists will pass up a "real chance" to inflict a Commons defeat on the Conservatives if its MPs do not oppose the move, she said.

She told Mr Robertson: "Although Sunday Trading Law is devolved, you will be aware of the concerns of the Union of Shop and Distributive Alliance Workers and others that retailers will pay for these extra hours by cutting pay in Scotland.

"I was alarmed to read reports over the weekend that the SNP have struck a deal with the Government that would see you tacitly support these proposals by failing to vote against them. This would constitute a major u-turn and workers across the country would rightly feel betrayed.

"I therefore urge you to give a firm public commitment that you will vote with the Labour Party and safeguard workers’ rights in Scotland and across the UK by opposing the devolution of Sunday trading legislation."

A vote on the law, which is also opposed by religious groups and expected to provoke a rebellion among some Tory backbenchers, will take place next week.

Hannah Bardell, the SNP's business spokeswoman, said that the SNP had never been opposed to the principle of Sunday trading and welcomed concessions from the UK Government.

She added: "Without the strong and principled action of the SNP, such protections may never have materialised. On behalf of the SNP I have met with and engaged with a wide range of interested stakeholders in recent weeks and will continue to do so in the run up to report stage of the Bill before we reach a final position."