Andy Burnham is against the Government's plan to relax Sunday trading restrictions

The Labour leadership contender says the rules benefit the families of workers

Andy Burnham is running for Labour leadership (Getty Images)

Restrictions on shops opening on Sundays should not be weakened, the frontrunner for the Labour leadership has said.

Andy Burnham said Sunday trading laws were important for families where parents worked in shops and that he would oppose the Government’s move to liberalise them.

“Sundays are only day people who work in shops can bank on some time with their kids,” he tweeted. “I will oppose this all the way.”

The Government is expected to announce a weakening Sunday trading laws in the Chancellor’s Budget, to be delivered tomorrow.

Large supermarkets have restricted hours on Sunday (AFP/Getty)

Rules currently allow smaller shops to open all day but shops over 280 metres squared cannot open for more than six hours.

But small business minister Anna Soubry said today that Sundays were previously “the most miserable day of the week” before laws were relaxed to their current level.

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"We are of that generation where Sunday, truthfully, was the most miserable day of the week,” she told BBC Radio 4’s Today programme.

The laws were temporarily relaxed for eight days during the 2012 Olympics as a trial.

The four contenders (clockwise from top left): Jeremy Corbyn, Liz Kendall, Andy Burnham and Yvette Cooper (Rex)

The shopworkers’ union USDAW is opposed to the change. John Hannett, its secretary general, said trade unions would campaign against the move, claiming there will “not be any economic benefits”.

Mr Burnham’s pledge could be an attempt to win favour with the union – which has a moderate leadership and endorsed David Miliband for leader in 2010.

The union’s backing could make up for the lost endorsement of Unite, Britain’s largest trade union, which endorsed left-winger Jeremy Corbyn.

Mr Corbyn and Mr Burnham are two of four contenders for the Labour leadership, the others being Yvette Cooper, and Liz Kendall.

Mr Burnham received the most support from Labour’s parliamentary party during the nominations phase of the contest, though there have been no reliable polls of people likely to vote in the election thus far.

Update: Liz Kendall has also come out in favour of the status-quo