Vote with your feet.
I've done the majority of my shopping at Lidl for the past 5 years now and and I can do a basic weekly shop for about £25 as opposed to £40 previously at Morrisons/ASDA. Once you get accustomed to the different names on their products it becomes second nature.
The big four rely on dumb shoppers who think big brands are everything. The sort who say "they've got to be Heinz baked beans or it's got to be John West tuna". You may not believe this but all those beans grow in the same soil and all that tuna is caught in the same seas whether it's John West, Princess, Morrisons own or imported stuff at Lidl. The sooner people wise up to this the sooner they will see their weekly shopping bills decrease.
I used to work with someone who wouldn't touch own brand products or go anywhere near Lidl or Aldi. A prime example of her was having to buy Old El Passo fajita kits. They cost over £3 but you can get own brand or similar kits at Lidl for half that. I mean, how specialist a product is a flour tortilla that you have to pay double for it?!
Supermarkets own brand is just big brand products in different packaging. Supermarkets don't manufacture anything, they just sell it. Can you imagine if supermarkets did manufacture all their own branded products? Every square inch of the UK would be covered in toothpaste factories, wine bottling plants, food processing plants, bakeries, aerosol manufacturers etc etc etc.