By Guy Taylor BP has forecast “broadly flat” oil and gas production in the third quarter, alongside a hit to profit from falling refining margins. The oil giant also said it expects net debt to now come in higher, driven primarily by the impact of weaker refining margins and the rephasing of around $1bn (£766m) of divestment proceeds in the fourth quarter. In a trading update, BP said it expected to take a hit of between $300m to $400m in third quarter profit due to a sharp drop in refining margins. Oil trading will also be weak, according to the firm. Realisations in its oil production and op…