"I don't know if sex is allowed at Cambridge. Is it?" Thousands of fans in foldable chairs and floral headbands cheer their reply.
"Oh good," Richard Thompson says, before launching into Johnny's Far Away, his 2007 ode to adultery. Such a civilised scene, soundtracked by details from life's murky underbelly, perfectly sums up the UK's premier folk festival, now in its 43rd year and still hugely successful. Thompson's Saturday show is the weekend's highlight. His voice and guitar have never sounded so rich, while his encore with comedian Stephen Mangan, a soft trawl through Fairport Convention's Who Knows Where the Time Goes?, provides the festival's most surprising moment.
The 2011 lineup also shows how folk works for musicians of all ages. Moore, Moss, Rutter – three technically gifted teenagers with boyband looks and banter to match – turn William Taylor's Tabletop Hornpipe into a tent-filling dance number. Twentysomething Emily Portman's stunning set is Bible-black, immersing us in a world of tongue-tied birds and magical coats made of moss. At the other end of the age bracket are Port Isaac's Fisherman's Friends, 10 Cornish shanty singers whose collective roar carries the might of the waves, a sadly underwhelming Pentangle, and Australia's wonderful Spooky Men's Chorale. Their Sunday children's concert may be more silly than spooky, but watching little faces in rapture at lyrics such as "we can grow beards if we want to" is something rather special.
More experimental delights lurk elsewhere. Sam Amidon plays with his voice like an avant-garde Will Oldham. Newcomer Jo Burke arranges child ballads around discordant keyboards and violins, while Sam Lee reinvents travellers' songs with tempered gas cylinders and a Japanese koto. From here, it's a big leap to the peculiar but popular booking of Rumer on the main stage – although songs such as Aretha carry dark, despairing depths – and the full-on Afropop assault of Femi Kuti, whose set is ripe with sex and politics.
A well-tempered comeback set by Mary Chapin Carpenter ushers on the final headliner, Laura Marling, who receives a scream-laden, stadium-sized welcome. Her Iron Maiden T-shirt and smart skirt also speak volumes: here is a musician now with steel in her spine, playing new country-rockers such as The Muse and old songs such as Rambling Man with fire and grace. "This is the only festival in the world that I could play this alone," she smiles before the new ballad Night By Night reveals just how special this weekend really is.
