Nerdish is a word, not particularly british.
In this case, it's a reference to a song by german hip hop group Fettes Brot, "Nordisch by Nature" (Northern by Nature). It's their most popular song, in fact, and what launched their career in the 90s. Fettes Brot is synonymous with hip hop in germany (though they're not really as "hip" as they used to be), and the song Nordisch by Nature is even more ubiquitous than they are.
That said, Nordisch by Nature is a fairly nonsensical song and the title is actually an intentional phonetic transliteration of "Naughty by Nature."
(EDIT: forgot to mention that the artist is german, for those who didn't notice)