Pretty serious stuff.Google says you'll be forcibly deported if you're not already in the queue for your transport home and are normally barred from the Schengen Zone. Maybe a bit harsh but those are the rules we chose.
Especially for those Brits with second homes.
I know of a couple of couples that now have to be careful about their time in EU, and rotate their presence on some occasions, i.e. one in EU, while the other is in UK.
They're fortunately retired and can afford it.