Just had a call from Amex fraud department, apparently the transaction was "pended" again so Tesco still haven't got their money even though the shopping got delivered no problem after they put the transaction through again.
I politely let the agent know how annoyed I was to have received this fraud warning and asked why it coud have happened.
Apparently they do know the details of the flights I booked and use the info for fraud detection purposes!
I suppose it's a good thing when it works, but annoying when it doesn't.