Replies to invitations are sent on good-quality cream or white writing paper. It is usual to use paper with a letterhead, showing the sender's address, and to reply in the third person.
Sample replies are as follows:
Mr and Mrs William Brown thank the President and Council of the National Society of… for their kind invitation for Saturday, 12th February, which they accept with much pleasure (or: which they have the honour to accept).
Lord and Lady White thank the Master of the Worshipful Company of Clockmakers for his kind invitation for Saturday, 12th February, which they much regret being unable to accept.
(A reason may be given, for example, owing to a previous engagement, because of absence abroad etc.)
The organisation of a large function is greatly facilitated by the use of reply cards, which should always be printed. The cards are sent out with the invitations and should be of small postcard size.
Guests should always use the printed card for their reply. Should they wish to add anything, such as an explanation for their inability to accept, this should be done in a separate letter.