You would think that Richey Edwards from the Manic Street Preachers carving “4 real” into his arm, in 1991, might have ended the British fascination with credibility. Yet the issue has grown, especially now that our leading musicians have stopped trying to sound American and started flaunting their regional accents. Just look at the Mercury prize nominations: Arctic Monkeys with gruff stories about Sheffield, Klaxons barking on about Dalston, and the East London council estate slang of Dizzee Rascal.

Now the 20-year-old Londoner Nash follows in that sarky slipstream with a debut album about bad boyfriends, best friends and big boozing – yet cynics have been asking if she is 4 real, too. Perhaps it is her fluttering dark eyelashes, or excellent piano playing, that lead them to wonder if her potty mouth and cockney intonations are genuine.

Well, she did study at the showbusiness BRIT School, but it was a free BTec, and she still lives at home in Harrow, North London – an area much less salubrious than its public school. She wrote these songs in her teens, and some might question her releasing an album so soon. The date was rushed forward to meet demand from her frenzied teenage fans and peers. But listening to the song Mouthwash, with its lyrics “I use mouthwash/ Sometimes I floss/ I’ve got a family/ Sometimes I drink cups of tea”, you do wonder if those fans couldn’t have waited until she had more than just five minutes to work on it.

Yet much of the record is glorious, and blessed with deep musical pockets. We Get On has a lovely doo-wop vibe, though Nash raging about sleazy tarts doing nasty stuff down at the park might ruin it for you if you are on the “eurgh, yeasty” side of her vocal Marmite divide. It all goes a bit Billy Ocean on S*** Song – “You could come round mine/ We could drink some wine/ In the summertime” – but soon reverts to typical Nash: “I think I might just drink the bottle myself/ Darling don’t give me s*** ’cos I know that you are full of it”. Elsewhere, Nicest Thing is a violin-stained weeper on which she finally, show-stoppingly, admits: “Basically I wish that you loved me.”

On the basis of this record, half the country will.

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