I would always take these 'family shop for £50' claims with a pinch of salt. Unless you are seeing what they are buying.
I think if you have time to shop around and get a few bits here and others there, then yes, you could save. Most people don't have time for that and how much are you spending on fuel/travelling between different places.
Lols, just as I post this
What do you rate in the frozen veg range as I am never particularly impressed?
Totally agree it's easier to cook cheaper in winter though!