Yet, come the service itself, only three people were singing the hymn at all; Kirsty, the vicar and one elderly lady at the back. The mourners didn't know it at all, although in fairness they sort of picked up the tune by the third verse.
A hymn may have been a favourite of the deceased, but it's the living who need to sing it, and if they don't know it, it can be embarrassing.
At Singers for Funerals, we always lead the hymn singing when we can, but we do need advance notice of the hymns to avoid that heart-stopping quick learn scenario, possible for foursquare hymns but a nightmare for modern tunes that jump all over the place!