Made for the UK
Scrannr is built in the UK, for UK shopping. Yuka is French in origin, and while it's officially available here, its scoring engine is the European Nutri-Score, and independent UK reviews report that supermarket own-label lines (Tesco, Sainsbury's, Asda, Morrisons) are hit-or-miss in its database. One app is designed for your shelves; the other works on them.
Data: open and UK-focused
Scrannr runs on Open Food Facts, the open, non-profit "Wikipedia of food" that anyone can inspect or contribute to, with real UK coverage (~190k UK products). Yuka runs on its own proprietary database, which it built in January 2018 after starting on Open Food Facts. Yuka's database is larger globally, but it's closed, and its UK own-label coverage lags. For open data focused on the UK, Scrannr's foundation is the stronger one.
Additives & scoring
Both apps give a 0–100 score. Scrannr has a strong additives database and flags what's worth a second look in plain English, so you get the picture without a blunt penalty deciding it for you. Yuka publishes a transparent formula (60% nutrition, 30% additives, 10% organic). That Nutri-Score basis marks down nutritious whole foods like cheese, nuts and olive oil, though, and a single additive Yuka rates "high-risk" caps a product at 49/100 no matter how little is present, an approach dietitians have criticised. Either way, treat the number as a quick comparison, not a medical judgement.
What's free
With Scrannr, product search and dietary profiles are free, you get five full analyses a month, and nutrition and allergens stay free. Yuka's core scanning is free too, but its search bar is locked behind Premium. The everyday features a UK shopper reaches for most are free on Scrannr and paid on Yuka. When you upgrade, Scrannr Premium is £2.99/month or £14.99/year with a 3-day trial for unlimited analyses; Yuka Premium starts at £10/year.
Privacy
Scrannr keeps your scan history on your device and needs no account. There's no login and no server-side profile of what you've scanned. Yuka is independent and states it doesn't sell user data, a real strength, but it does require an account, and your scan history is stored against it. Both beat ad-funded trackers; Scrannr is the more private of the two by design.
In fairness: what Yuka does that Scrannr doesn't
Two honest points in Yuka's favour. It also scans cosmetics and personal care, which Scrannr doesn't, since we focus on food; if you want one app for your shampoo as well as your snacks, Yuka has the edge. Its global database is also larger, which helps outside the UK. If those matter more to you than UK focus, free search and on-device privacy, Yuka is a reasonable pick.