Thom Yorke plays a new song, “Supercollider”, at Malahide Castle

Thom Yorke sat down alone at the piano at the start of Radiohead's second encore at Malahide Castle, outside Dublin, on Friday and played a song nobody had heard before. It was not on the band's written setlist. Dublin was the start of the European leg of the In Rainbows tour, and on Saturday, the second Malahide night, Yorke played the song again, alone at the top of the second encore once more.

The band had been working on it at soundchecks, Stereogum says, and calls it “Supercollider” (Drowned In Sound writes “Super Collider”). It has a piano figure in a major key that falls away into a descending minor passage, and a bridge. A reader's tip reached Drowned In Sound on Saturday morning, and fan footage of the Friday performance went up on the site the same day.

Colin Greenwood has posted a video on Dead Air Space, the band's blog on radiohead.com, of Yorke and Jonny Greenwood playing Portishead's “The Rip” backstage in St. Louis, where the band played on 14 May, three weeks before Dublin. Yorke reads the words off his MacBook.

Vulture's music round-up today puts both songs at the top of its list, and reckons Radiohead have found a new way to leak a song, by playing it to a crowd.

“Supercollider” at Malahide Castle