Not sure when the 250 feet rule was introduced (I think mid 1990s), but in the North Sea ranges area, I often saw various military aircraft well below 250 feet over the sea.
From the 1950's up to the early 1990s, I used to spend quite a lot of free time at Warkworth, where my folks had a place. Many memories of sitting on the sand dunes, watching Hunters blasting away at a drogue towed by a Meteor, in the '50s, through to Buccaneers heading back to Lossiemouth, and Phantoms and Jags, along with stuff from other NATO forces, flying back and forth.
The 'haar' is more of a cold fog, whereas a 'fret' is more of a summer mist, but yes, 'haar' is often used in the Northumbrian dialect, along with many other words that our former Colonial cousins would puzzle over !
Pull up a cracket hinny, and I'll tell yasall an aarful story .........