The dressing room of Camden's Electric Ballroom in London is hardly the most glamorous of settings at the best of times, and for Royal Blood it is the early evening after the night before. The previous night, the blues rock duo played its biggest ever headline show at the venue and, preparing for an encore later tonight, are disgruntled at the untidy state that greets me. "I'm sorry about the mess," offers drummer Ben Thatcher (26), politely.