Would you still be in the mood for a Mars bar if it came with a photo of someone getting open heart surgery? Experts suggest cigarette-style warnings on the nation’s favourite chocolate bars could help tackle obesity.  Similar pictures have adorned tobacco products since 2008 and are credited with pushing smoking rates down in the UK in recent years. Now experts from Cambridge University have shown that cigarette-style packaging would also put people off junk food. Seven in 10 people chose a piece of fruit over a Galaxy, Mars, Dairy Milk or Snickers that had a graphic label, in one test of the tactic.  Messages alerted them to the risk of…