A hangar full of analysts and investment bankers must have spent the long weekend formulating advice for Shell chief executive Wael Sawan for and against a takeover of BP. On the plus side, Shell’s strong share performance, reflecting its undiluted focus on oil and gas and boosting its market value to £150 billion, makes a bid look almost bite-sized – BP’s value having shrunk to £56 billion over the past two years as investors decried the commitment to renewables that its board has belatedly reversed.