Can an eBay UK seller sell long expired food items if the sell-by date is visible somewhere on the screen?

as far as I know there is no actual law that past dated food products cannot be sold, it is only that the possibility they are not still good to consume could be a problem.

As long as its clearly displayed, or it's explained that it's out of date, or even that its not for consumption, then I can't see an issue.

There are food items that have expiry dates, that don't really require them. Salt is one.

I thought we only do that in the U.S.

Possibly with canned goods, but not anything dairy or plastic wrapped.

HELL NO , THAT IS ILLEGAL

as far as I know there is no actual law that past dated food products cannot be sold, it is only that the possibility they are not still good to consume could be a problem

Of course. A person looking does not have to buy and if they do, then it falls on to them to either bin or resell.