For the best value per gram of protein in the UK, MyProtein Impact Whey is the cheapest mainstream option when bought during an Impact Week sale — on a discount code it drops to roughly 36p per 25g of protein, which is among the cheapest cost-per-protein figures of any UK whey. For the most widely trusted quality pick, Optimum Nutrition Gold Standard 100% Whey consistently leads on independent review scores and is the recommended choice for most buyers who want the most-reviewed protein on the market. For stable, transparent pricing without relying on sale codes, Bulk Pure Whey is the most consistent mid-tier option.
Supplement disclaimer: This article compares protein powders as food supplements on factual criteria (protein content, price, taste, ingredient transparency). It does not constitute nutritional or medical advice. Protein supplements are not a substitute for a balanced diet and are not necessary for most people. Consult a qualified healthcare professional or registered dietitian before making significant dietary changes, particularly if you have any underlying health conditions.
Comparison Table
| Brand | Product | Protein per 100g | Price per 100g | Cost per 25g protein | Informed Sport certified |
|---|
| MyProtein | Impact Whey | ~72g | ~£1.20 on sale | ~36p (sale) | Some batches |
| Optimum Nutrition | Gold Standard 100% Whey | ~77g | Higher — see note | Higher per 100g | Yes |
| Bulk | Pure Whey | ~71g | ~£1.68/100g stable | ~59p | Some batches |
| Applied Nutrition | Critical Whey | ~80g (4-source blend) | Mid-tier | Competitive | Yes — Informed Sport |
| NutriSport | 90+ Whey | ~90g | ~39p/25g in bulk | Among cheapest UK | No |
Prices checked August 2026. Protein powder pricing changes constantly with sales and discount codes — always verify current prices before purchasing. Cost per 25g of protein is the most accurate way to compare value across different bag sizes and protein percentages.
Best Value on Sale: MyProtein Impact Whey
MyProtein Impact Whey is the UK's most-bought protein powder, delivering 72g of protein per 100g with a sale-floor cost of roughly £1.20 per 100g during Impact Week and payday code drops — the cheapest mainstream whey concentrate in the UK at that price. The important caveat: MyProtein's "RRP" prices are inflated — never buy without a code. Wait for 40%+ off sales for genuine value. MyProtein runs near-constant promotions, but the "full" price is not a realistic reference point. Across 90 days of price tracking, MyProtein Impact Whey's lowest UK price varied by 47 percent depending on whether an Impact Week code was active.
Best Overall Quality: Optimum Nutrition Gold Standard 100% Whey
Optimum Nutrition Gold Standard is the most-recommended muscle-building whey in the UK in 2026, delivering 24g of protein and 5.5g leucine per scoop. Optimum Nutrition Gold Standard delivers 4.6 stars across 55,000+ Amazon UK reviews — an unusually large review base for a single product, representing a genuine signal of sustained real-world satisfaction rather than a small sample. It's available from Amazon (£34.95 for 900g), Holland & Barrett (£41 for 900g), and Optimum Nutrition direct (£40 for 900g) — Amazon is typically the most competitive third-party retailer for ON, particularly on Prime.
Best for Consistent Pricing: Bulk Pure Whey
Bulk Pure Whey delivers 71g protein per 100g with transparent pricing that rarely fluctuates — roughly £1.68 per 100g at sale floor, without the dramatic swings of MyProtein's discount-code model. Bulk wins on consistency and 5kg bag pricing. If you want a reliable monthly cost without monitoring discount codes or planning your purchases around Impact Week timing, Bulk is the more predictable choice.
Best for Tested Athletes: Applied Nutrition Critical Whey
Applied Nutrition Critical Whey is the Informed Sport-certified mid-tier option — 24g protein per scoop from a 4-source blend. The right pick for tested athletes who need certified batch testing but want better value than Optimum Nutrition Gold Standard. Informed Sport certification means each production batch is tested for substances banned in sport — relevant specifically for competitive athletes subject to doping regulations, not necessary for recreational gym users.
The Real Cheapest UK Protein in 2026
As of August 2026, the cheapest mainstream whey protein in the UK by cost per 25g is NutriSport 90+: a 5kg bag at £58.99 from London Supplements works out at about 39p per 25g of protein, from a British manufacturer that has been making protein since the 1980s. Less well-known than the flagship brands, but a legitimate product from an established manufacturer — worth knowing for price-sensitive buyers who've done their comparison properly.
How to Compare Protein Powders Accurately
Cost per 25g of protein is the only fair way to compare a 76% powder in a 5kg sack against a 68% powder in a 1kg tub. The gram-per-gram protein percentage (g of protein per 100g of powder) combined with the current price per 100g gives you the real comparison — not the bag price, not the per-serving figure (serving sizes vary), and not the "was/now" discount claim.
Flavour Realities
Protein powder flavour quality varies more by batch and reformulation than most brands acknowledge. Frequent flavour reformulations affect MyProtein's taste consistency review-to-review — a flavour that scores well in one batch may taste different six months later. Optimum Nutrition's Gold Standard is consistently cited for reliable flavour quality across batches, which is part of why it maintains its dominant review rating over many years.
How We Chose
We weighted protein content per 100g, real cost per 25g of protein (the only fair way to compare bags of different sizes and purity), Informed Sport certification, flavour consistency across batches, and Amazon UK review volume as a proxy for sustained satisfaction.
Frequently Asked Questions
See the FAQ section above for guidance on whether you need protein powder at all, the difference between whey concentrate and isolate, and whether vegan protein is a reasonable substitute.
