Salted or unsalted butter I'm a fan of James Martin and have no problem with the amount of butter that he uses.  However, I'm totally unsure what type of butter to use!  Salted or unsalted?
It really depends on how much salt you like in your food.  Most recipes are written for unsalted butter because it makes it easier to control the amount of salt.  If your butter is salted, you can use it and it will probably still taste good.  Although, you may need to reduce salt a bit elsewhere in the recipe if it uses a lot of butter.  When in doubt, go with unsalted, then add salt as needed.