An amber warning for extreme heat has been issued by the Met Office for Thursday, as some parts of England face temperatures of up to 38C. According to the Met Office, "The Fire Severity Index (FSI) evaluates how severe a wildfire could become if one were to ignite under current weather conditions." Most of London will be facing an 'exceptionally high' fire risk (Image: Natural England)Areas with an exceptionally high risk includes parts of both north and south London, such as Harrow, Dagenham, Romford, Wembley, Finchley, Croydon, Sutton, Stains-upon-Thames and Twickenham. Parts of London under 'very high' risk includes Wandsworth, Putney, Fulham and much of central London.