Aldi appear to list the prices, perhaps just a subset, I'm not sure: https://groceries.aldi.co.uk/

I shop there 2-3 times a week and wouldn't really say "rapidly". Or if they do, the swings aren't big enough for me to notice.

Though looking at their site, I think they are partaking in the old "raise prices for a short period then show them as a 'sale' price" nonsense. But it only seems to be £0.10-£0.30 and the higher prices aren't even that offensive (yes I have a soft spot for Aldi :D).

I would like to see companies forced to show the period that the higher price was charged for.

My local Aldi (London) has e-ink shelf end labels now, so they are at least preparing to change prices more rapidly.