Antoine Préat performs at St Martin-in-the-Fields, June 13 [@Benjamin Ealovege]

IT­ only happens once a year but it’s big, it stops the traffic (more or less), and it happens next Saturday, June 14, when the London Symphony Orchestra take over Trafalgar Square for a free concert of rockstar proportions – this year with an operatic theme, which means Verdi, Rossini and Puccini.

Antonio Pappano conducts. It starts 5pm. And you don’t need a ticket, just turn up – though it’s as well to arrive early to get a decent spot as far as possible from the noise of passing buses. lso.co.uk

• Something else that only happens once a year is Proms at St Jude’s in Hampstead Garden Suburb – which doesn’t start until Jun 21, so I’ll run through it all on this page next week. But meanwhile, check the programme: promsat­stjudes.org.uk

• Music@malling is one of my favourite festivals, running down in Kent in the charming little town of West Malling. But as it’s a train ride away, you’ll find it easier to go to Wigmore Hall, June 14, when the musicians at the heart of the festival, Chamber Domaine and their director Thomas Kemp, bring a taste of it to London. There are three concerts across the day, very much in the eclectic spirit of Malling with baroque music alongside new works. wigmore-hall.org.uk

• Another musician associated with an outside-London festival is the pianist Tim Horton who is part of Ensemble 360: resident group at Sheffield’s Crucible Theatre and responsible for its annual chamber music festival. He has a Wigmore Hall recital, June 17, where (without the rest of the Ensemble) he plays Chopin, Schumann, Stockhausen. wigmore-hall.org.uk

And keyboard fans should also know that the young French pianist Antoine Préat, one of the City Music Foundation’s star alumni, plays at St Martin-in-the-Fields, Jun 13. Busoni, Prokofiev, Ravel. citymusicfoundation.org

• Otherwise, it’s an overwhelming week for choral singing, the algorithms steering every choir under the sun into the same concert slots. Hampstead Chamber Choir sing Bernstein’s Chichester Psalms at Hampstead Parish Church, Jun 14: hampsteadchamberchoir.org. The Lacock Scholars have a creation-based programme at St Mark’s NW1, Jun 13: lacockscholars.org. And Camden Choir sing Dvorak’s Mass in D, June 14, St Mary’s Primrose Hill: camdenchoir.london
Meanwhile, The Sixteen bring their latest Palestrina programme to St James, Spanish Place, June 18: book through wigmore-hall.org.uk. Tenebrae launch a new CD of English choral music at St James, Piccadilly, June 19: sjp.org.uk. Westminster Abbey Choir sing Mozart’s C Minor Mass at the Abbey, June 17: westminster-abbey.org. And the Tallis Scholars are at Cadogan Hall, June 17 & 25, with a programme called The Earth Moves – because it features works that carry a punch: Tallis’s 40-part motet Spem in Alium, and the so-called Earthquake Mass by 16th-century composer Antoine Brumel. cadoganhall.com

• If that isn’t enough earthiness, the Earth Unwrapped series at Kings Place continues June 14 with entrepreneurial violinist Daniel Pioro leading a two-hour “spatial performance” through the building, kingsplace.co.uk

And coming down to earth with a bump, Lehar’s racy Merry Widow is up to its familiar (though always loveable) tricks in the Opera Holland Park season, Jun 19-28. operahollandpark.com