Most people compare protein powder prices by looking at the total cost of the bag. That's the wrong metric. A £30 bag can be better or worse value than a £50 bag depending on how much protein is actually in it and how heavy the bag is.
The number that matters is: how much does it cost per 100g of powder? Here's how the major UK brands stack up.
The methodology
All prices below are based on the current cheapest available price across tracked UK retailers (including active discount codes where applicable). I'm using the price per 100g of powder — not per 100g of protein, which introduces another variable (protein content per serving varies between products).
For a live view of the cheapest current prices, use the comparison table.
Whey concentrate (budget tier)
This is where the best value lives. Whey concentrate typically sits at 70–82g protein per 100g of powder and costs £1.40–1.80/100g at the best UK prices. MyProtein Impact Whey and Bulk Pure Whey consistently compete at the bottom of this range.
The cheapest I've seen for a reputable brand is around £1.35/100g during a major MyProtein sale with a stacked discount code. That's hard to beat.
Whey isolate (mid tier)
Isolate is more processed — lower fat, lower lactose, higher protein per 100g (typically 85–92g). It costs roughly double the concentrate: expect £2.50–3.50/100g for a decent isolate.
Whether the premium is worth it depends on your situation. If you're lactose sensitive or tracking macros very tightly, yes. If you're just trying to hit a daily protein target cheaply, concentrate is fine.
Casein (slow-release)
Casein digests slowly, which is why it's popular as a before-bed protein. It's typically more expensive than whey concentrate — around £2.00–2.80/100g. Optimum Nutrition Gold Standard Casein is the market leader and can be good value via Amazon when on promotion.
Vegan protein
Plant-based protein is almost always more expensive per 100g than whey, partly due to processing cost and partly because the market is smaller. Expect £2.00–3.50/100g for a decent pea/rice blend. MyProtein's vegan blend is among the cheaper options.
The honest conclusion
If price per gram is the only thing you care about: buy the biggest bag of MyProtein Impact Whey or Bulk Pure Whey you can find during a sale, with a discount code. That's the cheapest high-quality protein available in the UK, and it's not particularly close.
Check the live comparison table for today's prices — I update it daily so the numbers above may have changed. For today's discounted products, see the deals page. For a broader value guide, read best protein powder UK 2026.