It’s completely normal for muslims in Britain to celebrate Christmas. Don’t even think about questioning that. If you go to a mosque on Christmas day they will probably be singing carols and marvelling at the christmas tree.
Nobody is surprised that Mary Berry’s Christmas Party featured a muslim guest, because we have come to expect such things. Reality and ideology clashed though because almost all of the recipes included either alcohol, or pork, or other non-halal meat. As a result poor old Adil couldn’t eat much more than a canape at the party.