not sure what you mean.. it always asked me what i'm paying with.. i think that is the page your at now.. i put in visa, and my card number and info, and it takes me to the sage pay page..
how are you getting stuck there? i mean, watts it saying to you when you get there? are you sure your putting in the right card type as i think they have like 3 or so options just for visa's.. one for say debit and one for credit and another one that i would think must be for brits as i don't have a clue what it is.. make sure your putting in the right card type, visa via star i think is one. or the other one for a debit card if that is what your using..
if your still having issues, just copy and paste what its saying and delete your details of course first, and put it up here and we'll see if we can't get it straightened out for you..