Video footage posted on Instagram by bassist Ross MACDonald shows drummer George Daniel bent under a clothed table quickly puffing away on a lit cigarette and passing it to frontman Matt Healy, who turns to Ross and puts his hand to the camera when he realises he's being filmed.

According to the video, they hid another table during Ed Sheeran's performance, which featured a surprise collaboration with British grime star Stormzy, and Matt emerged from under the table as the audience began applauding at the end of Ed's set and joined in clapping himself.

Smoking inside London's 02 Arena is illegal under U.K. law which banned smoking in enclosed spaces in 2007.

Earlier in the ceremony, they won the Best British Group prize over the likes of Radiohead, Little Mix, Bastille and Biffy Clyro.

Accepting the award, Matt said, “This is mental. We’ve been a band since we were 13, for 14 years now. The only thing we tried to do with our album was to get back to that place where music made us feel alive.

"And I just want to say… people in pop music and in the broader public consciousness are told to stay in your lane when it comes to social issues but don’t do that, please don’t do that."

They had also performed their single The Sound and many viewers thought they had been hacked as messages criticising the band flashed up on screens behind them and on the TV broadcast such as "Do people really still make music like this?", while another took aim at singer Matt Healy's "terrible high pitched vocals". However, it was all an intended part of the performance and the messages were taken from their music video for the single.