Laurence Fox, St. James Theatre Studio, London

He has an amateur’s commitment and skill

“Hi, I’m Laurence,” says Laurence Fox, with the sort of awkward informality actors use when everyone in the room knows their name.

The son of James Fox and co-star of Morse spin-off Lewis - prime-time shop-window for a restless screen and stage presence - is here with a guitar in his hand, headlining a new cabaret evening in his very much lesser guise as a singer-songwriter.

The shaven-headed 34-year-old has a rangy physicality and headstrong attitude that suits rock just as well as acting. He followed the family tradition of getting chucked out of Harrow, smokes, drinks, and says what he thinks.

But the list of actors who’ve truly committed to music stops with Juliette Lewis; when Joaquin Phoenix seemed to, it was a conceptual joke. Fox’s apparent refusal to exploit his celebrity for a record deal is admirable, but the guitar he keeps by his side in theatre dressing-rooms is an outlet, not obsession. He has an amateur’s commitment and skill.

“There’s a £10 prize for whoever can guess who this song’s about,” he jokes, before a song naming and adoring his wife Billie Piper. One of his pleasant differences from professional musicians is not trying to deny every song is completely autobiographical.

His unpractised voice, though, cracks when pushed, going from gravelly to grating, subtly sweetened on high notes by his band’s guitarist. Red-faced and veins bulging, he sings better in gentler verses. But this isn’t just a vanity project.

Fox’s songs aren’t bad at all, revealing a fiery emotional life with arresting turns of phrase. “Don’t fall in love if you don’t want a gunfight” is fair warning, and lyrics about a relationship he’s now outside describe sacrificial, doomed romantic manoeuvres, summed up in the grim metaphor: “It’s so hard to build a house in the dark.” “Rise Again” runs the gamut of an affair that doesn’t, and does, “come to blows”.

An unfinished song perhaps sums up his freewheeling, high-strung life: “I know I’m wrong/ But I can’t change.”

Fox has taken the stage two hours into the first mixed-bag, mid-week cabaret bill at the new, Buck House-neighbouring St. James Theatre’s studio.

He rounds off a decent evening by dragging on Starsailor’s James Walsh. This pro has the vaulting voice Fox lacks, but worse lyrics. The actor’s songs remain an unassuming side-line for a charismatic performer.