Price promise guarantee .. could it work against consumers?

Papagena

First post! so apologies if this is not the right place.

I am starting to wonder whether this 'price promise guarantee' Tesco and Sainsbury's have (among others) could be just a way to get more money out of already cash-strapped consumers.

An example:

Tesco Everyday Value mushy peas
Last October : normal price 8p
April this year: normal price 15p
Now (August): normal price 20p

... and ... surprise ... Sainsbury's basic mushy pea is also 20p now!

It's a small example, but has anyone noticed unreasonable price increases lately, and also a trend of having the same price applied by different supermarkets for the same item? Could this just be price fixing?