Theatre with lyrics hits a high note

When is a musical not a musical? When it's a "play with songs". You may have spotted this phrase lurking – a touch apologetically? – below the title of new plays from some of British theatre's finest. First came David Greig's Midsummer, a delicious romp-com which had the two leads sling on guitars and sing about hangovers and bondage at climactic moments. The music and lyrics, by Gordon McIntyre of Scottish indie band Ballboy, were printed in the back of the programme, fanzine-style.

Then came Simon Stephens' Marine Parade, an elegiac drama set in an ailing hotel where lovers drift together and apart. This time the songs came courtesy of American Music Club's Mark Eitzel, who performed them with a jazz band from the back of the stage. If the playwrights weren't so fearful of the m-word, you might call them hipster musicals.

There's always been a tension between musical and "serious" theatre, snobberies of lowbrow versus highbrow, jazz hands over hand wringing, box office versus budget. The debate over musicals squeezing dramas out of the West End has become an annual tradition, falling somewhere between panto and al fresco Shakespeare on the theatrical calendar.

Stephens, creator of brutal modern classics Pornography and Punk Rock, had a typical playwright's antipathy to the tits-and-teeth world of show tunes. "The story in musical theatre is simplistic and saccharine, and the music is never as compelling or bold as in the rock'n'roll tradition," he says. Having worked on Marine Parade for four years, though, he came round to some aspects. "While I think there's something pernicious and slightly vile about things like the oeuvre of Andrew Lloyd Webber, there's something magnificent about A Little Night Music."

The boundaries are blurring all over theatreland. Enron had a blinging West End aesthetic, with its singing traders, while Posh had the bibulous Riot Club barbershopping Dizzee Rascal and Wiley between courses. Before that, Black Watch tingled the spine with rousing regimental songs amongst the swearing and gunfire. Even Jerusalem threw in a couple of folk anthems.

None of these is a musical, but they are all plays with music. In Jerusalem and Black Watch, it enhanced the mood, while Posh's plummy grime pointed up the anachronism of 21st-century students cavorting in 18th-century tailcoats. There's nothing new about that; everyone from Aristophanes to Brecht via Shakespeare knew the value of a good tune to delineate character or break the tension. Filter's masterful Brechtian Twelfth Night retooled the play as rock concert, reading Feste's songs as the heart of the revels and not, as so often, an inconvenient sideshow. Enron, similarly turned its drama into a deliberate spectacle. We already knew the ending after all.

The difference with Stephens and Greig is that the songs are not device or arch, Glee-style theatrics. They reveal the characters' inner lives. The songs, slow-burners rather than rafter-raisers, are there to serve the script and not the other way round. Belting 'em out is banned, yet they evoke the same visceral reactions as the best show-stoppers. "With Midsummer we got a much more emotional reaction than anything I've ever done," says Greig. "When a musical works, it hits you in the heart and the gut."

Plays with songs hit a happy middle ground, then: musicals for people who don't like musicals, plays for people who don't like plays. More than that, they're symptomatic of a cross-pollination where ballet dancers pirouette to pop songs on sets built by sculptors, plays are crossed with art installations and gigs have film backdrops. "We're the first generation of playwrights to have rock'n'roll in our DNA," says Stephens. "It's not about reimagining musical theatre, it's about using the live energy you find at a gig." Clearly, it's time to redraw the boundaries of theatreland – or, better still, scrap them altogether.