So it becomes clearer to me how the offer works. When a spend registers for avios the total spend from 18th june is calculated and an item is added to your account ...

In my case one transaction took me through both the 15k and the 20k thresholds, so 750 plus 750 ntps are waiting for my monthly avios sweep into my ba account.
They are not there yet, I expect them in the next couple of days.
And while some of you may think I'm a 'high roller' I just have had two large expenses that happened to be timed exactly right for the offer, it's bread and water for the rest of the year

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