The problem with DD is that payment is taken as late as possible (ie on the due date) which is not what you want if interest is running.
As you suspect, any payment you send will pay off statemented transactions before unstatemented transactions. This means that having made your £10 withdrawal, the £10 you send would be applied first to £10 that was on your previous statement and still waiting to be paid off. Meanwhile interest will continue to run on the ATM £10.
I use Clarity extensively abroad for cash. I don’t use DD. Within a few days of each ATM withdrawal, I pay off the entire balance by faster payments. This includes any purchases I have made too. That way I’m only paying pennies.
You could put your purchases onto a separate card that also doesn’t load foreign transactions (Eg Santader Zero – also good for cash, Post Office Mastercard etc). That way you can get longer credit on your purchases.
Whatever you do, remember to take backup cards (even ones that charge). Also I suggest you don’t run yourself low on cash without making the next withdrawal in case you have a problem. Cards are more prone to being blocked when used overseas, whether or not you tell you bank in advance.
If you retain the DD, be sure to understand how it interacts with manual payments.