Rockers GREEN DAY have prompted rumours of a secret side project, after fans realised new music released under the name FOXBORO HOT TUBS sounded remarkably like the band.

The group are currently working on a follow-up to their 2004 disc, American Idiot, but the stark similarities in vocals between Green Day front man Billie Joe Armstrong and those on the Foxboro Hot Tubs EP have got Internet blogs wondering whether the Holiday hitmakers have gone undercover to experiment with a new 1960s-inspired sound.

If Green Day are proven to be behind the Foxboro Hot Tubs, it would not be the first time they have released tracks under a pseudonym - in 2003, Armstrong, Tre Cool and Mike Dirnt dropped their techno release, Money Money 2020, under the name The Network.