There is no standard practice

RBS Group (RBS, Natwest, Mint etc) all do this, take the DD in full irrespective of whatever payments have been made.

Barclaycard will reduce the DD by the amount already paid off, assuming it clears a few days before the DD is due

Santander will not take the DD irrespective of how much, or little, has been paid beforehand

Personally, I prefer the Barclaycard approach but ultimately as long as you know which approach each of your cards take then its possible to deal with it. I got an annoying late payment fee because the Mrs spent £5 by accident on a santander and decided to go into the bank to pay it off which then meant the DD didnt collect and the £5 wasnt the minimum payment.