US oil giant ExxonMobil is planning to undertake a major overhaul of Britain’s largest refinery at Fawley on the Hampshire coast worth an estimated half a billion pounds. The £500m upgrade plan, if approved by the local authorities, would enable Fawley to produce more high-quality diesel to offset the rising demand for European imports. Fawley already fuels around one in six British vehicles. The 3,000-acre site makes up a fifth of the UK’s refining activities and processes around 270,000 barrels of crude oil a day.