If a couple of years ago, some old bloke in dungarees with a long grey beard had proclaimed that the Agnostic Mountain Gospel Choir were his new favourite band, you probably wouldn't have taken much notice. But this particular hirsute gentleman is none other than the now legendary Seasick Steve, a man who has somehow morphed from unknown street musician to someone who can single-handedly make a Royal Albert Hall audience feel like they are in his own backyard.