Some time ago British Airways stopped allowing people to open frequent flyer accounts. Strange, I know.
You had to book a full fare coach ticket to be eligible to join Executive Club (and then discount coach tickets still only earn a fraction of flown mileage).
At the time I advised folks to just go ahead and open British Airways accounts ‘just in case’. You never know when you might need one, such as when Jaguar was offering 10,000 miles for a test drive (and since you can combine 4 accounts in a household, you could earn 40,000 miles from the simple promotion).
It turns out that another way to get a British Airways account is to get a co-branded British Airways Visa. After all, the points you earn from that Visa need somewhere to go.
But apparently they’re also letting Diners Club card members sign up for BA accounts in order to transfer Club Rewards points into British Airways miles. And I can’t imagine there’s any way to check who is and is not a Diners Club cardholder.