I need to buy just over £5k of BA flights on my card tomorrow, but this will take me over the credit limit.

The online AMEX page has been saying that my balance will be collected by DD from my bank account on 25/8/08 (today).

I only have about £3.5k worth of credit limit left.

I'm presuming the DD payment will not have cleared AMEX by tomorrow as these things normally take about 3 days.

Is it possible for me to pay some money by debit card onto the AMEX card? I don't want to miss out on 15,000 BA Miles here!