Result
My son received an email from Canadian Affairs as follows:
Dear Mr .........
You are indeed entitled to EC 261/2004 but only now that you have made reference to them and requested it. They do state that it is only when referred to that you should be entitled. As you have made reference to and directly requested compensation in line with said regulations I have cancelled your free flight offer.
As full and final compensation you have been awarded €600 which equates to £480; this has been refunded to you via your original method of payment which will take no longer than 10 days to process.
Regards
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It is interesting that they state you have to mention the relevent legisalation in order to receive financial compensation.