Often only 10% discount at my local Tesco, max 20% except evening/Sunday afternoon bread products significantly cheaper.
Tesco usually do 3 sets of reductions
Morning say 10am ish, 12-25%
Afternoon around 2pm, 25-50% ish
Evening around 7pm, blanket 75%
Aldi and Lidl seem to both do 30% during the day and then 70% an hour or so before closing.
Sainsbury's and Morrisons seem more random
M&S used to be the worst for taking off a pittance, but I feel that Tesco are now in this position.
which cleverly don't have sell-by dates on the packages
All the fresh fruit and veg ive seen that supposedly no lonfer has a sell by date does, but it's clevely coded so instead of saying 04/10, it now says something like J4 (J being the 10th letter ie October, and 4 for the 4th). At least I've noticed that with things like sealed bags of apples and pears in Tesco and with bags of carrots in Sainsbury's.
It used to be the 7pm 'battle' as they would gather up all the stuff around 6pm, stick another yellow sticker on them and put it back out at 7pm. There was always a bit of a rush to get the best deals - one of the cheapest I ever got was some pastries (can't remember now but I think it was pork pies) marked down to 1p. Apparently they couldn't mark them as free as they had to have something to scan. Biggest percentage discount was the big £5 boxes of strawberries marked down to 20p.
Of late I think they've starting putting things out at different times to avoid the scrum.
I understand during the pandemic, the unions put pressure on management due to various incidents with reductions being put out and 'scrums' developing, though such incidents have been mentioned before in the media
One staff member I know told me there was an agreement to transition away from putting reductions out to customers and in future items would be offered to staff and charities only.