Assuming this is not a wind-up, what bit of "revenue based status" don't you understand . You have* to spend £28,653 to get 28,653 nTP

* - okay there are a few other ways to earn nTP, such as cabin bonuses, Amex spend bonus, although I think that has expired now. But this is a small amount in comparison. You will have to spend pretty close to £28k.

To give you a useful answer to the question, a BA Holidays trip in premium cabins maximises the amount paid, for nTPs given.