When I booked a 2-4-1 trip recently, using a voucher from my amex account, I had over 100k avios in my EC account, and my partner had 30k odd in his. We're linked as a household account.

I only had approx 80k avios deducted for a 100k flight, so I thought I'd been undercharged. When I finally managed to persuaded hubby to log into his EC account we found the remaining 20k or so avios had been taken from his account. We both had avios remaining in our accounts.

So I'm wondering, how do BA decide which EC account to deduct avios from when it's a household account? It's not a problem as such, but it's just one of those things that might be useful to understand for future bookings. Why weren't all the avios taken from my EC account, given that I had enough, I'd made the booking, and I was using my amex voucher? Do BA take them in date order, perhaps?