I purchased some US Currency from Amex last week. I could not buy over £700 worth using my BA amex card. This was despite being able to buy more than this amount in May this year and having a £15000 limit.... I called Amex and they told me that the credit cards now have a £650 limit per day and using the card is treated as a cash withdrawal. As always Amex do not treat it as cash and I get the points and £650 towards my £10000 per year spend for the companion voucher. Very strange ....
I had a similar issue with both my BA Amex and the wife's BA PP Amex - although our limits were lower and would have meant getting charged for delivery. I ended up using my Amex gold which appears to have a much higher limit for cash.