But one can look at this desperate improvisation another way. The Chinese string quartet playing Mozart so brilliantly in the sunken courtyard of Covent Garden Market offer a pertinent historical reminder. Classical serenades were designed to accompany eating and drinking, and chamber music in Beethoven and Schubert's time was played in drawing-rooms and taverns. Vienna didn't get a purpose-built concert-hall until 1831. Dr Burney defined chamber music in 1805 as not being intended "for the church, the theatre, or a public concert room". It was an intimate, cosily convivial art: Haydn playing for his royal patron, or groups of friends playing without any audience at all.
And chamber music was wonderfully portable. It still is, which is why it's increasingly being taken into hospitals and prisons, why cruise liners include resident quartets, and why shopping malls provide them as a feel-good incentive. Stockhausen's helicopter-borne string quartet may be little more than conceptual art, but it too reflects the artform's power of suggestion.
In time of war, chamber music crops up all over the place - as an entertainment for troops at the front, as a morale-boost for beleaguered citizenry (Myra Hess's lunchtime concerts in the National Gallery) and as a triumphal treat for tyrants (Jewish musicians playing in Auschwitz). If restaurants were not hampered by the necessity for a live-music licence, we would probably be serenaded over our food as Habsburg princes were in the 18th century.
Up till now, however, chamber music has played no part in the culture of that key British institution, the pub. Pub entertainment means rough stuff: rock, folk, cabaret, lager-lout "comedy", and a bit of jazz if you're lucky. Chamber music is not even considered suitable for pub theatres, though there seems no good reason why.
Sounding out the most convivial of them - the King's Head in Islington - I found it had never crossed their minds to stage a chamber concert, but, now that I'd mentioned it, they liked the thought. Would I be interested in filling their 96-seat auditorium for a series of Monday lunchtimes?
You bet. This Monday, a fledgling (but potentially top-flight) group called the Hengrave Quartet will play Beethoven and Dvorak in the pub's well-soundproofed space; the week after, a baroque trio - viola, harpsichord and viola da gamba - will play Handel, Biber and Telemann. Despite the token remuneration (a simple box-office split with the bar) and the fact that it is their responsibility to man the door and lights, these players have jumped at the chance, and not just because the acoustics happen to be perfect.
Taking their name from the Suffolk summer school where they met under the tutelage of the Palestinian-Jewish maestro Yfrah Neaman (with whom two of them are still studying at the Guildhall), the Hengrave Quartet are well used to playing in strange places.
First violin Adam Summerhayes says his best performance to date was when he took a pile of sheet music up a hill in the Lake District, and played for all the hikers who happened along; cellist Jonas Tauber has played Bach Suites for bored fellow-passengers on an overnight train in France; and violinist Yi Wang once earned himself a seat on the packed train from Peking to Shanghai by serenading everyone with Kreisler over the loudspeaker system.
They have played in the National Theatre foyer, but don't like it much: the trouble there is that the audience are preparing to focus on whatever it is they have come to see, and only lend half an ear.
On the other hand, Tauber used to moonlight in a cafe in Colorado, while working as principal cello in the Boulder Philharmonic. "I didn't mind people talking. Playing Bach in that cafe liberated me - it forced me to work harder to draw them in, and clarified my thoughts about the music. Those nights when people were hollering at each other, not listening, I realised it was personal, my own deficiency." Summerhayes disagrees: "Trying to force an audience to respond just brutalises your playing."
And talking of strange venues, Summerhayes reckons there are few things stranger than a string quartet in a modern concert hall, particularly if the audience is sparse. A string quartet is essentially four soloists engaged in a complex dialogue, with the audience an implicit eavesdropper, and it needs an intimate space. "The acoustics of a large hall can play havoc with your fine-tuned intentions. While the louder notes get into the acoustic and reverberate, the quieter ones can get completely lost."
Hans Keller once described the quartet as "an esoteric symphony" - a symphony in miniature, for cognoscenti. The more esoteric a truth, he added, "the more absolute the need for its immediate experience". He was arguing the need for people to play chamber music, as well as listen to it, but that was back in the less philistine Fifties.
There are signs, however, that the tide is now turning. Roger Chase, principal viola with the London Chamber Orchestra, sees the task of taking chamber music to places where people traditionally enjoy themselves as a social crusade. "Why should the bulk of the populace regard this civilised - and civilising - art as the preserve of a privileged few?"
While Pam Chowhan, concert planner at the South Bank's Purcell Room, reluctantly cuts the number of debut concerts - "there's no point getting young artists to come and play for a handful of people" - the youngsters are taking steps to work out their own salvation. Catherine Martin, the leader of the trio playing at the King's Head on 17 July, regularly stages her own concerts at a church in St Pancras. "It's very hard to find people who will actually pay you to play chamber music," she laughs.
Kiranpal Singh, Europe's leading exponent of the santoor (Indian harp) is one of those who does get to play in the Purcell Room, but when he brings Indian classical music to the King's Head on 31 July, it will be an earnest of his desire to plant the flag in new spaces.
Is this an idea whose time has finally come?
n Chamber at the King's Head: 10, 17, 31 July, 7 Aug. Performances begin at 1pm and last an hour. Tickets pounds 5 (concs pounds 3.50) at the doorReuse content