eteo,
I have brewed a limited number of Coopers kits: a Stout; a Dark Ale; and their IPA. The first two probably have used an identical yeast (they shared, more or less, identical directions). However, my IPA instructions say that this kit uses a Pilsner style yeast.
With that in mind, if you do the Dark Ale I'd suggest using the yeast from the Bitter...
EDIT: I stand corrected. A Coopers rep wrote to me and indicated that the yeast that comes with the IPA kit is an ale strain. The instructions mention some things about pilsner yeast and so I, in youthful exhuberance, understood this to mean this kit was supplied with a pilsner yeast. I will stop blushing and go hide in a corner.
Sorry if my post created any confusion for anyone.