Plan B, Roundhouse, London Jeffrey Lewis, The Haunt, Brighton

A cursory glance at the advertising billboards for the remake of The Sweeney, in which Plan B's Ben Drew plays the Carter sidekick role alongside Ray Winstone's hard-man Regan, might lead one to leap to all kinds of unpleasant conclusions. Young singer, a triple-platinum No 1 album under his belt, cynically parlays his pop fame for a movie career as a Professional Cockney, Dennis Waterman in a hoody.

This, of course, would be to ignore the entire jaw-dropping Ill Manors project: the song, the album, the film. In years to come his earlier album, The Defamation of Strickland Banks, may be viewed as one of the more peculiar sideways turns in pop history: a gritty London rapper making a slick retro soul concept album about a singer framed for a murder he did not commit. (When he's finally got it out of his system, that is: there's still talk of a Strickland Banks movie.) But for now, Plan B has returned to rap, with astonishing results. Last time he played the Roundhouse, at the height of Strickland Banks-mania, no one could have had any idea what he had up his neatly cufflinked sleeves.

This time, dressed down in denim, the Forest Gate boy is back to deliver something as incendiary as the pyros he detonates and the flare he brandishes around. Sure, there's still plenty to please the latecomers who only know him as a male Winehouse, showing off his improbably sweet falsetto on Strickland Banks singles like "She Said" and "Stay Too Long", as well as an encore which begins with crowdpleasing covers of Seal's "Kiss From a Rose" and Ben E King's "Stand By Me". But the real thrills, for anyone interested in Drew as a developing, evolving artist, come from the new material.

Ill Manors came as a sobering shot of social realism into a year of marshmallow-brained flag-waving, offering a bracingly grim view of council tenement life only a brick's throw from the fairyland of the Olympic Village. The extracts tonight, notably "Playing With Fire" (on which he's joined by Labrinth and support act Delilah), stand up strong alongside the more familiar hits.

To sugar the pill, it helps that Drew is an appealingly geezer-ish, ordinary-bloke presence, rugby-tackling his own guitarist for laddish laughs. He's probably as sick of comparisons with The Streets as they are, but Drew is essentially Mike Skinner with the latter's sentimental streak replaced by a political one.

"Ill Manors", the Shostakovich-sampling single and the climax of the show, is a work of sheer genius. Assisted by Yann Demange's astonishing video, it was a rightful and righteous Top 10 hit in April, one of the all-time great British protest songs, in the vein of "God Save the Queen", "Going Underground", "Common People" and "A Design For Life". Standing in the middle of a crowd chanting its toff-taunting chorus – "Oi! I said Oi!/What you looking at, you little rich boy!/We're poor 'round here, run home and lock your door/Don't come 'round here no more, you could get robbed for/ Real ..."– in the week when George Osborne was booed at the Paralympics is utterly thrilling: the Bullingdon brigade bullied back.

Jeffrey Lewis is a quirkaholic. The insanely prolific Brooklyn anti-folk singer is, to put it politely, an acquired taste, and it barely matters whether Jarvis Cocker is correct about him being "the best lyricist working in the world today", nor that tracks like "Don't Let the Record Label Take You Out To Lunch" and "Cult Boyfriend" have you thinking that he may have a point, when his idiosyncratic, quirk-overloaded delivery forces you to restrict your exposure to extremely short doses.

With his newly shaven pate and Rhodes Boyson mutton-chops, the 36-year-old Lewis and his band deal in simple, cheerful indie-pop with wilfully out-of-tune singing, reminiscent of the likes of Weezer, Jonathan Richman, Cake, Camper Van Beethoven and especially They Might Be Giants. Indeed, the "work, he/Turkey" and "soup/recouped" rhymes, no matter how skilfully crafted, cannot help but raise memories of They Might Be Giants' "on it/bonnet" from "Birdhouse In Your Soul", causing a violent allergic reaction in this reviewer.

Sometimes, too, his references are too parochial: his reimagining of Edgar Allan Poe's The Raven as being plagiarised from the work of a New York Jewish predecessor falls on stony ground among Brits who don't get the semitic slang.

But – and you knew a "but" was coming – he does have his moments of brilliance, invariably when he launches into one of his comedy-historical songs (10 of which have been used by The History Channel's website). These include the most succinct explanation of the Cuban missile crisis I've ever seen, illustrated by a PowerPoint presentation of cartoons from his laptop (Lewis is, in his spare time, a comic-book artist). Even better is his limerick-based "History of the Development of Punk On the Lower East Side of NYC 1950-1975", from beatnik Harry Smith to Patti Smith via half a dozen 30-second snatches of the major players (Velvet Underground, Iggy, New York Dolls) and the more obscure figures such as David Peel (whom I am now determined to investigate).

If this music thing doesn't work out for Jeffrey Lewis, there's a job waiting for him as the coolest high-school history teacher on Earth.

The mighty Dexys take their comeback album One Day I’m Going To Soar on the road, starting at the Barbican, London (today); Corn Exchange, Cambridge (Tues); Symphony Hall, Birmingham (Weds); and Guildhall, Southampton (Thurs). Meanwhile The Cult and The Mission co-headline at the Apollo, Manchester( Mon); Academy, Newcastle (Tues); Academy, Sheffield (Wed); Barrowlands, Glasgow (Fri); Academy, Birmingham (Sat); Hammersmith Apollo (16 Sep).