Premium cabin should rightly mean premium food even if it is a special meal. Mass catering options exist for vegetarians especially out of London.

As for Antigua, if the OP wants some recommendations for how to not eat meat or fish, let me know. Antigua is my favorite holiday destination and (hate to say it) VS UC is a much more fun way to start the holiday! And holidays are all about having fun. Will just have to earn the Tier Points some other time.