LONDON, Sept 7 (Reuters) – British Airways’ CEO said on Tuesday that negotiations to set up a new low-cost subsidiary at London’s second biggest airport Gatwick were “advanced”. “We want to set up a subsidiary which has got a competitive cost platform,” BA CEO Sean Doyle told reporters at an event at Heathrow Airport. “We’re in, you know, advanced negotiations to try and enable that.” The airline, owned by Anglo-Spanish group IAG, first announced plans for the new business focused…