By Heather Main Lulu flipped burgers there. Clash singer Joe Strummer and legendary DJ John Peel were regular customers. Brad Pitt is a fan, and comics Russell Howard and Joe Pasquale were spotted tucking into a burger just days ago. Wimpy, where millions of Brits had their first taste of fast food, celebrates its 70th anniversary in the UK this week. But with 63 branches still open, it is more than a trip down memory lane. The chain was first launched in Indiana, USA. But Chris Woolfenden, general manager of Wimpy UK, says: “I think there’s a real Britishness to Wimpy which is part of what ou…