The Barbican, a week before Christmas, and it’s British folk-rock legends Steeleye Span’s last gig of the year, a year in which its vigorous seven-strong line-up – featuring a new recruit in the shape of former Bellowheader Benji Kirkpatrick – celebrated a half century of Span by releasing a strong new album in Est’d 69.

What a jolting coincidence that one of the 20th century's angriest symphonic beasts should have a rare unleashing on a night of high national anxiety. Whether Vaughan Williams spewed forth his Fourth Symphony in response to darkening European clouds in 1934 or as a sublimation of sexual frustration, given his unhappy domestic life at the time, it hit us all hard last night.

“How many times have you heard the conductor sing?” asked William Christie after the final number, but before the two encores, of Sunday night’s 40th birthday celebration for his ensemble Les Arts Florissants. Well, lovers of old recordings know that you sometimes get plenty of impromptu vocalisation from the likes of Bernstein and Barbirolli.

There are encores and encores – most a friendly, minimal farewell gesture from the soloist; some a jolly, festive unwind after a particularly taxing piece. And then there’s the luxury free gift that Sir András Schiff bestowed on us during the second of two Barbican concerts with Iván Fischer and his Budapest Festival Orchestra.

This family concert – “Total Immersion: Lift Off!” – was basically a small-scale rerun of this year’s CBeebies Prom, that one entitled “Off to the Moon”. The Prom had a space theme, to mark the 50th anniversary of the Apollo 11 moon landing, and this Barbican concert just came in under the wire, still in the anniversary year, even if the commemorative events from the date itself, back in July, now seem distant.

A few years ago it would have been hard to envisage proto-punk maniac Iggy Pop being a star feature of the EFG London Jazz Festival. His last few albums, though, have been heavily flecked with jazz, and let’s not forget that as far back as The Stooges’ 1970 album Funhouse, free jazz sax squalling was part of the mayhem.

The megastars are here at the Barbican, for an intensive three days in the case of the LA Phil and Gustavo Dudamel, throughout the season as the hall shines an "Artist Spotlight" on pianist Yuja Wang. Despite a shallow opener showcasing the individual talents of the Los Angeles principals and daft, rollicking Sousa at the end, there was a seriousness of intent and depth of focus that belied the touring glitz.

Because he dramatised power, Shakespeare never really goes out of fashion. Treatments of his plays do though, and the RSC’s Measure for Measure, a transfer from Stratford set in turn-of-the-century Vienna, feels distinctly slack. The backdrop is supposedly a city filled with refugees, artists, political movers and shakers and members of the upper-class and demimonde.

When it comes to the true jazz legends capable of filling concert halls with faithful fans, whom jazz festival programmers can put on as headliners, the choice is dwindling. Herbie Hancock is one and he does; his Barbican concert is one of the big events of this year’s EFG London Jazz Festival and it had been sold out for months.

So much was fresh and exciting about Michael Tilson Thomas's years as the London Symphony Orchestra's Principal Conductor (1988-1995; I don't go as far back as his debut, the 50th anniversary of which is celebrated this season).