All that ever counts, regardless of "offer" or "saving" is the price per 100ml or kg. Thankfully the pesky EU interfered with the UK yet again and insisted that must always be displayed.
Haven't used Tesco delivery for years, but their "best offers" always brought back the 10p and 7% savings, the real savings were on different tabs or buried in search. There was a search by cheapest, never by price per unit. Funny that.