Don't use P@H as they're a rip off. Go to zooplus and like mentioned Orijen is the best you can get at £60 for 13.6kg, otherwise pick one of the slightly cheaper ones, Acana (owned by Orijen), Purizon, Markus Muhle (black angus, otherwise the cheaper one is the best one going if money is tight), Applaws etc. Just look at the ingredients and make sure it's not bulked out with maize and wheat (compare Orijen ingredients to Pedigree and you'll see what I mean). I just look in the special offers and buy whatever is best at the time, my dogs food get constantly rotated against most advice with no ill effect.
As for cans, buy the 24 x 800g Rocco or Lukullus for around £30. They're essentially the same as they're both owned by zooplus, the Lukullus just has some added herbs or some such. It's just minced offal, but I've seen big bits of ham in them at times that looked quite tasty hehe.
Expensive food isn't expensive as it's far more nutrient dense.
If you sign up to zooplus discount thing you get 5% off every time, plus they use DPD which is the best courier going with hourly slots and tracking.
You can go down the route of the independent like others have mentioned but it's how far down the rabbit hole do you want to go! I think there's only one major dog food manufacturing plant in the country (other than Mars and Nestle), so everything is made in the same place. Brands just go there, tell them what they want and sell it on.