Originally Posted by
bakera
Why not just overpay your card. E.g. pay a couple of £k into your account so that your available balance is £card-limit + amount-overpaid
Excepting asking AMEX to increase your limit (doubt that will be instant) then this is the best suggestion! If you "make a payment" on your AMEX via the app or website using a debit card then it is an instant posting to your account. If you do a bank transfer this is 24-48 hour to reflect on your account. So as above, make a payment using debit card of the amount you will need over your limit.