All invitations from the Sovereign are commands.
Replies should be worded to reflect this and addressed to the member of the Royal Household who has issued the invitation.
Mr and Mrs John Debrett present their compliments to the Master of the Household and have the honour to obey Her Majesty's command to luncheon on 8 October at 12.30 o'clock.
Note: the date of the letter is written in the bottom left corner of the paper
The reason for non-acceptance should always be stated. A prior engagement is not considered to be a sufficient reason for failing to obey the Sovereign's command.