Are corn meal, corn flour and polenta interchangeable?

Ok so I googled this and found nothing, so thought I would ask our lovely bakers and makers here.

I am hoping to make this sexy recipe: http://www.nigella.com/recipe/recipe_detail.aspx?rid=20421, But I do not have any corn flour on me. Is it possible to substitute polenta, or should I just use some plain flour?

Thankees.