Not sure how that would work, unless I'm missing something? You need to spend £30 to get the £5 discount, so can't get that on the main game as its £25, and the pass is £25 on its own, unless you are talking about buying the pass elsewhere?
Oh, I'm Polish and I didn't take currency difference into account, sorry for that:/
I need to spend 100PLN to be eligible for a 17.50PLN discount, the base game is 124.50PLN (that actually works out to under 25 quid with the current exchange rate) and the season pass also somewhere around that so in my case the discount applies to both. I just stupidly assumed that if I get a discount on a given purchase, everyone else around the world does as well:/
So yeah, in your case deluxe makes more sense.