The EU countries were supposed to have already introduced legislation banning a mandatory retirement age. At the Berlin summit in Nov 2002, the UK and France were taken to task for failing to introduce legislation. A final date of Dec 2006 was imposed at the summit. Failure to comply will mean that the EU will be able to take the countries to the EU court. Similarily, individual citizens will be able to claim compensation from their governments, through the EU courts, for loss of their right to continue working. Make no mistake - this legislation will come into force. The exact wording of the law, with all the variuos exemptions/exceptions has yet to be presented to parliament, but it will have to comply with everything in the EU directive which has been in existence for over ten years now.
BA, like every other employer in UK will have to change their mandatory retirement date.
As for the French/ICAO rules regarding a ban on Captains on international flights over the age of 60 - well the airline will have to use you on routes where you can legally fly. If the airline does not have enough routes avoiding France to give to old pilots, then the company would be obliged to terminate your employment - because there is no work for you to do. Clearly no employer will be forced to retain people who cannot legally do the job they are contracted for. They might choose to offer you a first officer's post, where flying over France would be legal, but presumably the rate of pay would be less, because the responsibility and experience requirements of the post are less.
Britannia are ahead of the game here. They allow Captains, the option to move to First officer at the age of 60.
Perhaps, in the next few years ICAO will change the aviation treaty, to allow international captains over 60. Then France would be out on a limb within Europe, and would be forced to comply with current JAA rules which do allow Captains over 60.