HMRC's A to Z names invitation cards, and acceptance cards with them. It is not the occasion that decides it, and a wedding invitation is in the same position as a corporate one. An invitation is kept until the day, often on the mantelpiece, so it fails the leaflet characteristic of being ephemeral, and where there is an RSVP to complete and return it fails 3.4 as well. The invitation that behaves like a leaflet is the one distributed in quantity to people you do not know: a flyer inviting the public to an open day is a leaflet, not an invitation card.
What decides it?
Sent to named guests and kept, or handed out to anyone and binned.
Where does this come from?
HMRC VAT Notice 701/10, section 8, HMRC's guidance on zero rating books and printed matter. See the notices we work from.
Some real jobs
100 wedding invitations with an RSVP card20%
Invitation cards are listed as standard-rated, and the reply card is for completion and return.
Invitations to a corporate launch20%
Same item, different occasion. The list does not distinguish.
5,000 flyers inviting the public to an open day0%
Distributed in quantity, held and read, thrown away. That is a leaflet.