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 it costs
This is where the two apps differ most. Yuka's core scanning is free, and its Premium, from £10/year, adds search and dietary alerts on top. Scrannr has no free tier: the app is free to download but not free to use. After a 3-day free trial it costs £7.99/month or £24.99/year, which works out at about £2.08 a month, roughly 74% less than paying monthly. That one subscription covers everything Scrannr does: unlimited analyses, product search, dietary profiles, supermarket browsing, nutrition and allergens, with nothing held back for a higher tier. If a free app is what matters most, Yuka is the one; if you want UK-focused analysis without a paid-feature ladder, Scrannr is.
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
A few honest points in Yuka's favour. It has a genuinely free tier: you can scan without paying anything, and Scrannr no longer offers that. Its Premium, from £10/year, is also cheaper than ours. It scans cosmetics and personal care as well, 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. And its global database is larger, which helps outside the UK. If those matter more to you than UK focus, included search and on-device privacy, Yuka is a reasonable pick.