Athlete/I Am Kloot, Old Royal Naval College, London

Rock festivals get everywhere these days. It seems every local authority with a small patch of grass wants to be in on the action, to earn kudos from having one or two mid-table bands play their back yard.

Some of these festivals are edgier than others – the hipster dollar only stretches so far – and the Greenwich Summer Sessions have been pitched to the "comfortable" end of the spectrum. When a band like Athlete headlines an all-dayer it's never going to end in riots, especially not in the Christopher Wren-designed heart of maritime Greenwich.

Six bands appear and all of them play sedate and agreeable sets to an enthusiastic crowd. Notably, the Manchester stalwarts I Am Kloot, fresh from a Mercury nomination, play a heartfelt set of songs from their fifth album, Sky at Night. They work well in a wider setting, expanding with confidence won from a large crowd and a bigger band, and they are beginning to sound like the heirs to Elbow they have always been supposed to be. They traipse off early, only for their singer, John Bramwell, to return and admit to being too blind to read his new set list. It's a sweet moment, typifying the band's shy charisma.

Athlete are locals, from Deptford, but they are still a strange choice to headline a festival, even one as unaffected by the vagaries of fashion as this. In fact, the immaculate 18th-century environs of the Old Royal Naval College rather suit the band. They have no pretensions and make no sops to spurious authenticity – they are just a gentle, indie-ish band playing a relaxed show to ardent fans in an entirely civilised milieu.

Athlete push no envelopes – their songs are largely sedentary 4/4 toe-tappers, simple guitar melodies supported by a warm buzz of lightly applied keyboards. They have acquired a horrible reputation for being also-rans in the Coldplay era and nothing could make me put on one of their records, but tonight that seems not to matter.