Barbara Cook is back in London, and all is right with the world. In fact, the only wrong thing about the entire exhilarating cabaret evening of fine songs, finely sung, is its slightly inaccurate and misleading title, Mostly Sondheim.

The selections are not even largely Sondheim; partially Sondheim would probably be more accurate, even if the rest of the programme's choices do have a tenuous link to the celebrated composer, in as much as they are all songs from a list of some 50 songs that he declared, in a New York Times magazine article, that he wished he'd written.

But it does mean that Cook, and her invaluable longtime musical director and pianist Wally Harper (looking more gnome-like than ever, but an unerringly supportive and utterly sympathetic player), have found themselves invigorated by a largely new repertoire. Sure, because it's on Sondheim's list, she's able to sneak in one of her signature songs, "Ice Cream", and make it sound as fresh as when she herself first introduced it nearly 40 years ago in Boch and Harnick's 1963 Broadway musical She Loves Me, though she amusingly points out afterwards that she had to "give that B natural more thought than I used to". And even though it's also on Sondheim's list, she avoids "Glitter and Be Gay", even though she, too, introduced that classic nearly 45 years ago in Bernstein's Candide - she's a singer who clearly knows her (considerable) strengths and (few) limitations.

Though the bell-like upper register that made her the leading Broadway ingenue of the 1950s and 60s isn't as powerful as it then was, Cook's tone remains exquisite, the notes sublime, her control effortless. Best of all, she connects totally with every lyric, and not just so that every emotion within it is revealed but also, crucially, so that every single word rings out in the theatre with utter clarity. Her superb technique is, of course, a given; but the overwhelming feeling that she also invests in the material is a constant revelation. She makes you hear these songs often as if for the first time. To hear Cook sing Irving Berlin's "I Got Lost in His Arms" from Annie Get Your Gun, for instance, is to get lost in a song that I thought I knew but suddenly realised I hadn't paid attention to its achingly lovely lyrics before. She achieves this effect with the utmost restraint; she never bullies the listener or the song, but simply draws you into the latter's world totally.

The Sondheim selections are no less revelatory, not least for the fact that - since his songs are character-based and have therefore often been rendered by performers who are actors first rather than singers - they're actually given their full vocal as well as emotional resonance. A powerful curtain call rendition of the title song to "Anyone Can Whistle", performed without a microphone, was so perfect and true that you could weep. I could go on; but you just need to go.

Mark Shenton