Invitations to the Prime Minister and spouse should always be sent in the form of a letter. It is not correct to send only a printed invitation card. This of course does not apply to private invitations sent to the Prime Minister and spouse by their families and close friends.
The Prime Minister or his/her spouse should not be invited to adjudicate in competitions, nor should they be asked to assist in the selling of tickets for charity or raffles. It is embarrassing for persons who either do not desire to purchase a ticket, or perhaps cannot afford it, to have to refuse them.