There is an economy and directness of resource, and the obvious lack of sometimes brash and confusing power available in a full orchestra, that can present first experiences to the listener in a persuasively unthreatening way. Especially before lunch, from 11am, after the Saturday night before . . .

Not that this regular monthly audience come seeking cushions and soft furnishings. A challenge is what they seek and enjoy, and a challenge somewhere in these programmes is what they regularly get, usually in the form of a 20th century work. But thus, it is never an ordeal.

The Elias, three times resident at the Britten Pears School, were naturally able to include Benjamin Britten's second quartet (Opus 36 No 2) in this programme. And to have a British composer taking his place among the usually mainland European music of this chamber concert series was a welcome reminder and assertion of the achievements from these shores in this genre.

Premiered in 1945, it is cast unusually from the outset, in three movements, with the weight biased towards the longest third one. Mysterious melodies and rhythms - were the reedbeds and breezes of the River Alde conjured up? - and exploration, purveyed the first movement. And a scherzo both daemonic and mercurial followed.

Then came a Purcell-influenced Chacony and a remarkable set of 21 variations on the foundation bass line, sectioned off by three cadenzas for different members of the quartet, and culminating in a final three in which Britten takes the four instruments onto an orchestral plane. The Elias sounded large and expansive, and far beyond the fields of Suffolk.

Framing the Britten were two items by Mendelssohn, to whom the string quartet seems to be an orchestra in miniature, with each instrument aspiring, with its notes, figures and sweeps, to sound like two or three of its own. And the influence of Beethoven is an easy catalyst for this.

The Elias confess to be especially at one in Mendelssohn's company and, to choose a name for themselves, they picked a nominal variant of the composer's most popular oratorio, Elijah.

Opening the morning, his Four Pieces Opus 81, in which the Elias brought the Eb Fugue forward, from the last to being the third movement. Thus, a return in key to the E of the other three movements, achieved a more classical unity. It comes from the last year of Mendelssohn's short life and the four movements were a happy conglomerate of separately composed movements, two of which had been unrelated.

Closing this concert in the round, after interval cake and free sherry for the audience, was Mendelssohn's earliest published quartet (Opus 13 No 2) in A. minor. The work combines elements that derive from a romantic Mendelssohn song and from his own responses as one of the first composers able intellectually to assimilate the late Beethoven quartets.

The quote from the song heading the score reads: "Is it true that you are waiting for me in the arbour by the vine-clad wall?" Which brings me to the element of passion.

Two French sisters combine, on first violin and cello, with a cool Swedish violist and a fiery Scot from Fort William on second violin. They are Sara and Marie Bitlloch (is that surname Ecossaise?), Martin Saving and Donald ("Where's yer Troosers?", sorry couldn't resist it . . .) Grant. And les girls lead the group in the performing passion stakes. Their electricity, which brought the men's own supportive responses, characterise the Elias.

All four are part of the larger Ensemble 360, who are now familiar faces, and popular, in this chamber music series, which continues on February 17 (11am).

It is then the Emperor Piano Trio, with young players from far eastern shores, So-Ock Kim (violin, Forea, the virtuoso Li-Wei (cello, China) and Naomi Iwase (piano, Japan). Their programme will bring piano trios by the Russian, Arensky, by Ravel (which draws from Malayan verse form), and conclude with Beethoven's "Ghost".

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The Elias and Ensemble 360 record for Sanctuary Classics, the Elias also for French label, Ambroisie.