Quote (re the minimum payment):
"All default fees, annual fee (if applicable), payment protection insurance premiums, and interest plus 1% of the remaining balance shown on your statement, plus any arrears payable (subject to a minimum of £5)"
Source:
http://www.santander.co.uk/csdlvlr/ContentServer?c=SANDocument_C&pagename=WCSUKPublicaLte%2FSANDocument_C%2FSANDocumentPreview&cid=1324580957647
Taking out £1500 in cash will cost you a 3% fee (£45), so you'll owe £1545 (assuming that you're starting from a zero balance).
So your first monthly minimum payment would be £15.45, leaving you owing £1529.55.
You'd then be charged 2.207% interest per month on the remaining balance, so your balance would actually rise to £1563.31 for the next month, requiring a minimum payment of £15.63.
. . . and so on!