All the above answers are correct, you don't earn Prem as it is invitation only. If I am correct you won't get ever get it off individual travel either, ECCA travel only. If the amount spent under the ECCA is enough then PERHAPS the firm will get one Prem. As for perks, the written perks are all the same as gold, it's the extra attention BA Special Services offers and the fact that they really honor the perks that make the difference.

Prem is one of those things where if you have to ask about it you won't get it...