Fire and ice. When the cool, steely tone of Joshua Bell's ‘Huberman’ Stradivarius met the feverish impetuosity of Pablo Heras-Casado at the helm of the London Symphony Orchestra  for the final leg of its International Violin Festival, it wasn’t always a case of opposites attracting. Sibelius’ Violin Concerto emerged as something of a tussle between soloist and orchestra which, although very much in the traditional nature of a concerto, sometimes felt uneasy. It was followed by a stop-start, slow-burner of a performance of Berlioz’s Symphonie fantastique that didn’t ignite until late.

After a few early intonation issues, Bell revelled in the sense of fantasy and poetry of Sibelius’ violin writing in the first movement Allegro moderato as one theme melted into the next. There was great technical assurance in the fierce double-stopping and long trills of the development section. Yet orchestral interludes tended to veer towards the brash, punctuating the narrative with angry outbursts. This was especially problematic in the tender slow movement, where Bell’s relaxed, lyrical phrasing was countered by brass playing which was just too intense and incisive. The jog-trot of a finale – christened “a polonaise for polar bears” by Donald Tovey – arrived at a happier compromise in approach, although it met with occasionally ragged orchestral co-ordination.

Untidy orchestral entries also marred the opening movement of the Symphonie fantastique, which was unexpectedly lumpen. Heras-Casado conducted without a baton, beating time sometimes with his right arm, sometimes his left, sometimes both, with tiny gestures to cue entries. Perhaps I’m too used to hearing lean, mean period bands tackle this wild work – “the first psychedelic symphony in history” as Leonard Bernstein described it, with typical colour – but the performance was weighed down by the sheer volume of string players (60 listed in the programme). This gave the “Daydreams—Passions” movement a soporific effect – no opium required! – smoothing contours and drowning woodwind detail.

Things picked up with a second movement waltz full of lilt, charm and delightful hesitations before spinning around the dance floor once again. Flautist Gareth Davies was fleet of foot, joined by a quartet of harps providing filigree detail. The rustic idyll of the “Scene in the fields” featured a rather rough-hewn shepherd (cor anglais solo), answered from an off-stage oboe which didn’t sound distant enough. The LSO strings once again bathed us in a warm pool of sound, until a quartet of timpanists enlivened proceedings as the storm clouds gathered ominously towards the movement’s close.

Kudos to the timpanists for injecting rhythmic tension into the “March to the Scaffold”. Although the bassoonists’ grumblings got lost amid the string pizzicatos, brass angrily pronounced their death sentence and the percussion department despatched our poet to his death with a mighty thud of the guillotine’s blade. The “Witches’ Sabbath” finale was the best of all, a cackling coven of woodwinds being outrageously gruesome. That so many violins could produce such spectral sul ponticello and spiccato effects is a marvel, the symphony closing in a heady bacchanale. If only the journey there hadn’t been quite so fitful.