Why does Phillips Crab taste like chemicals, unlike M&S's Orkney Crab that tastes natural?
A quick comparison of the listed ingredients shows only crab meat for the M&amp;S products (clearly visible in the photos in your question), whereas the Phillip’s website of the pictured product says:


  Ingredients: Crab Meat, Sodium Acid Pyrophosphate (SAPP) added to prevent the formation of struvite crystals.


Sodium Acid Pyrophosphate is also called Disodium pyrophosphate and the Wikipedia article states:


  Disodium pyrophosphate can leave a slightly bitter aftertaste in some products, 


In short, you taste something because there is something other than just crab meat. If SAPP tastes unpleasant to you, avoid products with it and choose ones without a preservative or with a different one (if a taste test is ok for you). In a pinch, masking the off taste may be possible, but not necessarily what you are looking for - you’d also be masking the crab flavor.