A bricks and mortar festival, Spitalfields is a celebration of that secret, early 18th-century buffer zone between the City and the East End and its great baroque basilica, Christ Church, whose restoration was the reason for the festival's existence until people realised that the arts don't raise money. They're just an agreeable way to lose it.

Still only half-restored, Christ Church makes an austerely impressive auditorium. By custom, the festival focuses on music of the building's period alongside music of today, and this week's programme featured two of the three composers who serve as Spitalfields' artistic directors, Judith Weir and Michael Berkeley. The big event was the premiere of Weir's new Piano Concerto, given by William Howard and the BT Scottish Ensemble; although "big" is perhaps the wrong word for a piece that sets out to challenge our 19th-century-fixed assumptions of what a piano concerto should be.

Far from some epic struggle of the one against the many, Weir's concerto is a return to the early Mozartian model of a chamber ensemble where the soloist leads rather than fights his colleagues. Written for an "orchestra" of nine strings grouped round the piano, it's domestic music, lasting merely 15 minutes. But the intriguing thing is that it uses the rhetoric of 19th-century Romanticism, softened and reduced. What you hear are grand gestures in miniature: a game with scale which is a characteristic of Weir's work. Much of the time she plays the game with humour: an ironic, deadpan mischievousness that supports her own assessment of herself as a subversive composer. The concerto doesn't have that (except maybe in the last, least successful movement); and the result is a piece that feels constantly in denial, dashing the expectations it sets up of climactic development and melodic resolution. To that extent it's frustrating. But it's also fascinating, haunting, and further proof of the gently maverick mentality that makes Weir one of Britain's most treasurable composers.

Michael Berkeley's Spitalfields spot came in a marathon double-concert of music for brass and voices featuring the Joyful Company of Singers: an ensemble whose name carries the chilling promise of finding them on your doorstep, armed with a smile and a text, but who are actually the accomplished winners of the 1990 Sainsbury's Choir of the Year Competition. Their Berkeley items included a sequence of beautifully crafted motets, a spectacular 1980 setting of "At the round earth's imagined corners", and a wedding anthem, "Love is strong as death", that sounded like a conversation between Messiaen and Andrew Lloyd Webber.

But the chief interest was a new Berkeley piece for brass quintet and reciter: a collage of love poems by the 17th-century Earl of Rochester called Fantastic Mind which laid a sometimes rhythmically notated spoken text across the music in manner of melodrama. Notated speech is a tricky, chalk-and-cheese medium which, in English, tends to sound affectedly like Walton's Facade - especially when vowels are stretched through long durations and the only way to sustain them is to inject a sigh into the voice. But Berkeley (acting as his own reciter, with the Fine Arts Brass Ensemble) somehow manages to keep everything anchored in dignity, and his settings are profoundly effective, with richly imagined part-writing for the brass that builds from overlapping waves of fanfares (objets trouves from the world of Britten's Owen Wingrave?) and settles into the sort of nostalgic astringency you hear at the end of Stravinsky's Oedipus Rex.

Garsington Opera is another celebration of place - the Jacobean manor house doubles as a scenic backdrop to the shows - but after eight years in business the festival needs to decide how central the location is to its artistic thinking. Does it go on being something pretty in a country garden or does it strive for something more?

The options were more or less spelled out in the first two stagings of its 1997 season. The first, on Monday, was the latest in the succession of obscure Haydn operas which Garsington has made its speciality; and like most of the others we've seen here, it was worthy, charming, but a touch dull. Le Pescatrici (The Fishermaidens) ranks extra-high on the obscurity charts in that its musical manuscripts were part-destroyed by fire soon after composition. But Wasfi Kani, Garsington's music director, has pieced the fragments together with borrowed arias from other operas, and the result is something that plays rather like Mozart's Cosi but for lower stakes: two pairs of lovers playing around with each other's fidelity, mixed up with a Cinderella-figure who gets her prince. Conventional stuff.

The pity was that Garsington did it so conventionally, with nothing in the way of design or production to bring the thing to life. There was attractive singing from Lynne Davies as one of the maidens and smart orchestral playing under Wasfi Kani's own hand - but otherwise very little to keep your mind off the picnic interval.

Cosi fan tutte, the next night, was a different matter - not least because of a striking set that obliterated the house, but made real theatre, thrusting the action forward into the audience's laps. The designer was Tim Goodchild, homing in on 1950s Dior haute couture; the director was Ian Judge, delivering his usual, ultra-professional package of energy, style and not-so-sly camp. We've seen Fifties/fashion-conscious/camp Cosis before, but this one was wonderfully distinctive, with strong, sharply observed characterisation, elegant chorus-work, and outrageously funny business in the medical scene - involving the biggest hypodermic syringe I ever hope to see outside a Carry On film.

With a superb ensemble of actor/singers - Richard Halton, Jeffrey Lentz, Janis Kelly, Cara O'Sullivan, Andrew Slater - this was a completely engaging show with high musical values sustained by Steuart Bedford: a conductor whose "nose" for Mozart struck me last year when he did the Garsington Idomeneo. My only reservation was the soprano Dorabella, who upset the pitch-symmetry between the pairs of lovers: you need one higher and one lower voice to each gender, especially if, as here, the Dorabella has a brighter sound than the Fiordiligi. But this Cosi is exactly what Garsington should be doing. Force-nine gales ripping through the audience tent during "Soave sia il vento" weren't ideal, but they were less distracting than the participation of Garsington's neighbours the night before: a barrage of persistent hedge-strimming, car alarms and (very stylish this) encircling aircraft, timed for maximum disturbance. I only hope the neighbours felt good about their efforts to ruin the hard-rehearsed performances of young singers trying to make careers. And I hope they like the way they're making their village a byword for risible small-mindedness. Not to say ruthless husbandry. If their campaign continues, there won't be a hedge in Oxfordshire left to strim.

Glyndebourne doesn't have these problems, but it is going through a rough patch with its casting this season. The Manon Lescaut was disappointing, and so is the Le Nozze di Figaro that opened last week: a revival of Stephen Medcalf's reticent production (in contrast to the raunchy period- update he has just done for ETO) which has previously been reliant on a sharp young cast to make its point. This time it's not so sharp. Apart from Ryland Davies's high-profile Basilio (who deservedly gets to keep his often-cut Act IV aria), the only memorable character is Susannah Waters's Cherubino: thin of tone, but done with touching, waif-like charm. Charles Mackerras conducts the LPO nicely enough; but the Age of Enlightenment Orchestra would be more interesting.

Spitalfields, E1 (0171 377 1362), to 25 Jun. Garsington (01865 361636), to 25 Jun. 'Figaro': Glyndebourne (01273 813813), Thurs & Sat, to 28 Jul.