There is interest payable if you take cash from atm on a credit card, but is it same for cash back from tesco?

Lets say i buy items for £25 using credit card and take £50 as cashback on same card from any store which provide cash back facility, do they consider as a single transaction of £75 or two transaction 1. shopping for £25 , 2. cash withdrawl of £50. if they consider a single transaction, its intrest free untill my due date otherwise £50 would be considered as cash taken from atm. i do not know answer yet and thats why its here.
Answer
Cashback on credit cards is usually not available at checkouts. i assume that it is because of this reason which you have highlighted. otherwise it would be next to impossible for the card issuer to differentiate which rate of interest ( normal or cash advance) they must apply to transactions.