So flights started to show again on Book a Flight page on app, so made it through to paying and after getting past the credit card bit apps has thrown an error.
Message says please contact us, so a call to Silver line in the morning I guess.
Amex has not flagged a transaction on phone, which usually happens before I get to see booking reference, so looks like they've partially fixed whatever problems they had earlier in the day.
My Bookings is not showing anything and no emails as yet.