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Have a look around online if your looking for anything Camelbak as 20-30% discount seems to fairly standard but still a little more expensive than Decathlons prices which are generally unbeatable for their price-performance across most of their lines. Check sizing for running packs as well as it'll drive you mad if it swings about or rubs anyway. Many come in at least 2 different chest sizes.
Thanks @Retro_Bastard, @Sainsburys_Ed and @hats