David Cameron has formally warned retailers against undermining the new national living wage, after it was found that Marks and Spencer had slashed Sunday pay.

Labour MP Siobhain McDonagh revealed that the retailer had made cuts to Sunday, Bank Holiday and anti-social hours pay, leaving around 11,000 staff up to £2,000 a year worse off. McDonagh urged Cameron to “close the loophole” during Prime Minister’s Questions on Wednesday.

The Prime Minister is adamant that retailers including M&S, ensure that the recent increase to the national living wage for workers over 25 should result in a higher overall wage, not lower as a result of cuts.

MPs have also previously critiqued B&Q, Bradgate Bakery, Morrisons, Eat and Cafe Nero for not abiding by the new wage through the creation of alternative terms.

“Approximately 11,000 of Marks & Spencer’s most loyal employees, many with over 14 years service, are about to get a serious pay cut” The Mitcham and Morden MP said.

“Cuts to Sunday pay, Bank Holiday and anti-social hours pay, all made on the back of a National Living Wage, means they’ll take home less next year than they do this year, with some losing up to £2,000.

“This is not just any pay cut. This is a big, fat Marks and Spencer pay cut.”

“Obviously we want to see the national living wage feeding through in to people having higher take home pay not lower take home pay” Cameron replied.

“We would urge all companies to make sure that is the case.

“I haven’t seen the information about Marks and Spencer. They know like any retailer that they need to attract and retain and motivate the staff that they have.

“And it’s absolutely crucial in retail especially with all the competition with online that they continue to do that and they won’t do that if they continue to cut people’s pay.”