Ok, good to know, I think what they are recommending is a dual purpose primer/undercoat but they are pigmented to match the paint that is going on top of them so tempted to just go for that (partly for convenience). Would go with Zinnsarr if it was going to make a huge difference over the own brand stuff. Just have no bloody idea!
EDIT. Have just ordered the Craig and Rose Primer/undercoat to for the woodwork along with all the other paint.