The following sequence should do the trick: wash the car well. Apply a special finish restorer like T-Cut (Automotive Chemicals Ltd, Bury, United Kingdom; phone: +44 161 764 5981) or Farécla G3 (Broadmeads, Ware, Herts., United Kingdom; phone: +44 1920 485548). These special products used to remove oxidation are available from car paint specialists—don't confuse them with the average All-You-Need-Is-Our-Product Magic Color Restorer available at gas stations and advertised by infomercials. As they work by removing the top, oxidized layer of your paint, reading and sticking to the instructions carefully is of utmost importance. T-Cut has a special variant for metallic finishes, Farécla can handle both.
Wash the car again very well to get any remaining restorer off the finish, then polish it with a good quality color restorer (like the Turtle Wax Color Magic series) and finally wax it (eg. Turtle Wax Hard Wax With Teflon or Hard Shell Shine Car Wax). Waxing the polish thoroughly requires some elbow grease and is therefore neglected by most, however, no wonder product claiming easy application can beat the shine and protection of hard wax. The liquid version of Turtle Wax is much easier to apply.
Certainly, you cannot use T-Cut or Farécla regularly as they would remove all the paint from your car. For everyday protection use hard wax or liquid wax, the color restorer should be used once or twice a year.