Monty Python have released a previously unheard song featuring the late member Graham Chapman, ahead of their string of live dates at London's O2 arena and a rerelease of the Monty Python Sings album.

Entitled The Lousy Song, it features Chapman and Eric Idle listening back to a swinging orchestral number that Idle has recorded, with Chapman lampooning his partner's efforts. Introducing it on Simon Mayo's Radio 2 show, Idle called it an "extraordinary, silly release... It was sort of improvised over a bad song I wrote. It's sort of unusual as it's Python improv, but it's cute because it's Graham, and it's very off the wall... I couldn't tell if it was funny or not. It's absolutely a sketch and not a song." After listening to it again, he said it was "very Morecambe and Wise."

Reading on mobile? Click here for video

Idle also elaborated on the forthcoming live show at the O2. "I've been working on it for eight months, so I've had more than slight anticipation - I've got sheer terror," he told Mayo. "I have to put this show together in some way, shape or form. I'm doing the lifting on this one. We always split [the work] up; I've done the stage ones traditionally. I've got to fill the O2 with a silly show. We've spent about three million quid on it so far."

He said the show's content was made up of the team's favourite skits from down the years, and that "we've got lots of young people and dancing and stupid songs." Of the stage decor, he said that "it's all Gilliamised", referring to the vivid, psychedelic work of Terry Gilliam: "A lot of strange art deco... 60s art, cut-out art... It's a huge carnival, it's enormous."

The sold-out run begins on 1 July, while the reissued album is released on 9 June. A box set of nine Monty Python albums, Monty Python's Total Rubbish: The Complete Collection, will also get a release on 30 June, with CD and vinyl versions alongside Terry Gilliam artwork and Michael Palin liner notes.