Kate Tempest, a 30 year old dramatist and poet, has an appeal that’s hard to fathom. Is it all in the elbows? Like most performers raised on hip hop, she recites with her upper limbs flapping and wiggling as if by remote control. For emphasis she uses that impatient downward flicking gesture, beloved of rappers, like a countess at a buffet ridding her fingers of unwanted guacamole.