Everything at my local corner-shop/grocery store is 30-45p more expensive ?

That's the same as all local or corner shops. You should always expect to pay quite a bit more as they can't compete with the big supermarket prices and stay in business. We shop at Asda ( 3 miles away) but if I'm in the middle of baking, for instance, and I discover that I have run out of a vital ingredient, I will use the local shop - 10 minutes' walk away. I know it will cost more, but it's more convenient than getting on a bus & going to Asda for just the odd item.