The big Tesco nearby has a single combined queue for all the 20 or so self-scan checkouts. They are rarely all in service. With a few items it is now always faster to go to an operator checkout unless you go in at 4am. The express lanes of "under 10 items" or "cash only" are a memory of a former, much faster time.

There is often an employee aggressively marshalling people to the self-scan checkouts at every available opportunity and trying to pull them away from the staffed lines.

In the local Pound shop they tried replacing all checkouts with self-scan, getting rid of all others. They had to reverse this a month or two later and put back half a dozen, now brand new, staff operated tills - ripping out a few weeks-old self-scanners to make space. They are again slower thanks to rarely having staff nearby to handle the steady stream of staff authorisations and errors, so there's a big delay every time someone wanders over from the back of the store to wave their bar code and immediately disappear again.