Justin Bieber has taken the unusual step of backing a charity single from a south London hospital’s amateur choir to beat him to the UK Christmas Number 1 spot.

The Canadian singer has called on his fans to help make Lewisham and Greenwich NHS choir’s charity single A Bridge Over You the top single over his own.

The NHS choir was just a few hundred sales behind Bieber’s Love Yourself when the pop star tweeted his unusual appeal to his 71.9m followers.

He wrote:

The song was originally recorded two years ago with Gareth Malone on the BBC2 programme Sing While You Work. But this year NHS choir member and children’s doctor Katie Rogerson and her colleagues started a social media campaign to get it to Number 1.

Proceeds from the NHS choir’s single will go to health charities including Carers UK and Mind.

Sales will continue to be counted until midnight on Christmas Eve, with the result announced by 1pm on Christmas Day.

The outcome is likely to be close but one thing that appears certain is that we won’t have an X Factor winner in the top spot this year.

This year’s X Factor champion Louisa Johnson’s Bob Dylan cover Forever Young entered the charts last week at No 9, selling just 39,000 copies.