LED rear lights were introduced when the facelift was released on April 1st 2006, all U.K cars prefacelift were fitted with xenons, facelift cars have bi-xenons. The rear led's are a 5 minute job to fit, cost around £300. Fitting Bi-Xenons means removing the bumper but they are plug and play. Cost, not too sure, I think at least £1,000 -£1,500.
Pete