The answer is the premium placed on branded goods. A tin of Heinz Baked Beans will 'carry' the cost of advertising and promotions. The own brand supermarket version, that can come out of the same factory, does not carry those 'costs' as the big supermarket involved will ordered a massive quantity with them telling the manufacturer what they want to pay. Negotiations between the manufacturer and the buyers of the supermarket will take place that basically guaranty the price, therefore profit margin, that will be available subject to, say 100,000 units being ordered by the supermarket.
In addition, if the manufacturer want to increase their output at the factory of a product, and/or it is going to be promoted, they will encourage the national retailer to order 100,000 units with a large discount given so that profit margins are at least maintained for the retailer, with of course the expectation that an increased volume of the product will be sold, all at full margin. This all results in the cash margin being maintained all the time higher volumes of sales evolve. Selling 100,000 units with a retail price of 50p, and a margin of 5%, results in a higher gross profit than just 1,000 units with a retail price of £1, and a margin 10%. So if your supermarket can sell 100 times more own brand product than the branded version they can retail it at the far cheaper price and obtain a healthy cash margin, with extra customer footfall taken away from the competition in the process.
You may already appreciate Ron that the major national retailers have tremendous leverage over the manufacturer and can almost dictate the price they will pay. My company used to attract massive bonuses, tens of thousands of pounds, every time the amount of stock ordered exceeded certain targets in addition to the margins already agreed. If you remember Tesco's even had certain manufactures crying out about how that supermarket had squeezed their margins (ah, poor souls
) and refused to supply them with anymore stock. In the end the supermarket won through as the market dictates what price is applicable for a certain product, with customers choosing the 'cheapest' offers. Farmers have had this problem for some time, with some supermarkets at least paying more for milk. But, once again, the marker decides the true worth of a product, and the retailer decides what margin of profit they need to keep their business viable.
The retail market is not for wimps, and can be a harsh master. Only the leanest, profitable business will survive as has been witnessed, and will continued to be witnessed, for ever in our capitalist system.