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.

cashback on credit cards is usually not available at checkouts. i assume that it is because of this very 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.