I've tried it before, admittedly two or three years ago and the booking just failed "there was a problem" - no 'sensible' message explaining what went wrong or a re-application of the discount.

That did make me think though - are sales like this really a good business investment for Visa? Well obviously they are, but who stands the cost of my 30 to 40 Euro saving? I'm guessing both A3 and Visa split it as they both benefit and there are probably behind-the-scenes fee discounts going on between the airline and Visa too. But is there really such a thing as brand loyalty between Visa and Mastercard, or whoever? I currently have four cards and I do try to have at least two different "suppliers" in case of a problem while travelling, but I honestly had to dig out my cards and look which was which (one Visa and three Mastercard). The thing is, I (and I suspect 99.9% of people) really don't care which one I use as long as it works.