Under the kind of picturesque sunset that has been an all-too-rare treat of late, Lily Allen's sunny reggae sound, sweet vocals and potty-mouthed lyrics filled the summer air of Somerset House's beautiful courtyard. Part of the Summer Series that also includes Amy Winehouse, Hot Chip and, tonight, Mika, it was a well rounded show that demonstrated the extent to which the singer has raised her game in the live stakes since releasing her debut album a year ago.

Opening with LDN, which was enhanced by her authentically Caribbean-sounding brass section, Allen looked confident and relaxed in a vintage white dress as she trotted out the ironically merry melody juxtaposed amusingly with lyrics depicting urban squalor. Her trendy teenage fans at the front screamed their appreciation, while the thirty-something types clapped politely.

Gallery: Lily Allen at Somerset House

Next up was one of my favourites, the endearingly silly Nan You're A Window Shopper, a witty little track based on 50 Cent's recent rap hit, Window Shopper. For me, this kind of track showed Allen at her best, singing cheeky lyrics that obviously reflect her sense of humour. Giggleworthy, if rather unkind, Not Big may have been a song about small penises, but it showed off nonetheless a richer, more controlled vocal technique than she's displayed in the past.

The same could be said of the tongue-in-cheek B-side, Cheryl Tweedy, on which she jokingly bemoaned her lack of a resemblance to the Girls Aloud star. Thankfully, however, unlike her Glastonbury performance of the song, last night's version contained no ranting against Tweedy, with whom she has been locked recently in an ongoing slanging match.

Despite this, it seemed important to Allen - or perhaps to her label - that she appear angry about something. Unlike Amy Winehouse, engaged in an ongoing battle to curb her drinking for the sake of her career, Allen strikes me as a fairly together young artist who feels obliged to engage in a bit of rebellion, also for the sake of her career. Between every song, the F-words flowed thick and fast, especially when she introduced Everything's Just Wonderful, a song whose aim was, she claimed, "to say 'f**k you to anyone that tries to f**k your s**t up". Got that, kids? In truth, she seemed to be scraping the barrel for things to rage about, decrying school bullies, mortgage lenders and that semi-compulsory pop bogeyman, George W Bush.

The show's highlight for me came when Lynval Golding appeared on stage to lead the band in a spirited rendition of the Specials hit, Gangsters. The song's bouncing ska rhythm had the crowd dancing, while her evident love of the music, and surprisingly good rapport with Golding, left me with the feeling that at last, we were listening to the real Lily Allen.