It's a project born of envy. The comedian Alex Horne first met the drummer Ben Reynolds and the trumpeter and banjo player Joe Auckland when they were all just a year old. They went to primary school together and became friends.

As they grew up and became established in their professions, the trio looked wistfully at each other's worlds. Horne liked the skill of musicianship: how, as he put it, you can whip out an instrument at a wedding and everyone will love you and dance. In the same situation, stand-up comedy can fall soul-sappingly flat. Music can drift into the background, but when a comedy gig goes wrong there is no escape. Everyone knows when a comedian dies on stage.

Horne's friends, meanwhile, were caught up in the earnest world of jazz (or playing for Girls Aloud, in the case of the saxophonist). Comedy seemed more fun. When Horne performed a successful stand-up gig at the Ronnie Scott's jazz venue in London, they decided to join forces.

And so The Horne Section was conceived - a mixture of comedy and jazz, jokes and trombones. Horne invites guests along to perform material (including Mark Watson, Tim Key, Tom Basden, Tim Vine and Doc Brown) and the band plays along. It's a simple idea, with daft results.

In Edinburgh, where the show made its debut last summer, Jimmy Carr spouted one-liners while the band kept rhythm underneath, sometimes slotting in a trill to round off a gag. "It was like the good equivalent of a 'ba-boom chhh'," Horne says.

The genres fuse naturally, he thinks. Both comedy and jazz have a natural rhythm and both demand an ease with improvisation. Sometimes the performers are all on the same wavelength; sometimes they're not. Either way, it seems to make the audience laugh.

But mostly it works because Horne and his friends are fascinated by each other's skills and enjoy playing together. ("It's not a deep, thought-provoking show," Horne says.) Furthermore, the musicians and comedians share a crucial attribute - both camps "quite like staying up late and drinking".

The Horne Section is on at the Lyric Theatre, London W1, every other Monday until 28 March