OK so this is the latest and worse case as it denied both seat selection and on-line check-in. And yes, my Exec C;ub number/status was recognised onbooking AND I could see it inside my Exec Club account.

So, if it's more understandable for a code share and Expedia booking to cause problems (though I frankly think in this day and age there is no excuse for this to be so ..

... WHY would I be denied on-line check in - more than 20% of the time - for direct bookings with BA on a BA flight where my Exec Club no is used at booking????

I'm sorry but something stinks in BA's IT systems at the least ..