Lorna, primulas germinate really really easily from fresh seed. I have never purchased a primula and they spring up all over the garden, even in the lawn!!
It is amazing how things pop us wahaj. I weed less now - unless it is obvious what the seedling is because so often the seedling is a worthy garden plant. I have teasles, pansies, echiums, angelica, geums, poppies, various daisies,cerinthes and many many more that seed themselves all over. I remove what I don't want, and the rest just add to the display! ;D