POLICE have reportedly launched an investigation into a sectarian video posted online by the brother of SNP MSP Derek Mackay.

The Finance Secretary’s brother Stephen uploaded a 30-second video of football supporters belting out the offensive song at an Old Firm game.

Posted onto Facebook, it shows hospitality guests roaring: “We’re up to our knees in Fenian blood, surrender or you’ll die.”

It was reportedly recorded at the League Cup semi at Hampden in October 2016 in which Celtic won 1-0.

Stephen’s fiancée is also captured singing along, although she is not seen on camera during the sectarian line.

“We have received a complaint and inquiries are continuing,” police said, according to The Scottish Sun.

Mr Mackay said after the video was posted that his brother is not a bigot, adding: “I’ve never heard him use any language like that or an attitude that would lead me to believe that.”