PUB landlord Billy Nettleton was astonished after a 700-year-old grave cover was discovered in his village pub - thanks to the smoking ban.
He knew nothing about the carved stone relic that had been built into an internal passage wall.
But one of his regulars, archaeologist Percival Turnbull, spotted it low in the wall as he stood outside puffing his pipe, because he can no longer smoke in the bar of the Blacksmiths Arms in Mickleton, County Durham.
Though the stone had been painted over, he identified it as part of a stone used to cover the grave of an important person, such as a merchant or successful craftsman in about 1300. Graves of less important people were not marked in that era.
Mr Nettleton said: "I've run the pub for ten years and walked past the stone many hundreds of times without noticing it. Nobody would ever have known about it, but for the smoking ban. I am really amazed.
"It is in a passage on the way to the gents' toilets. I opened up a door in the passage so customers could go out for a smoke. It was pure luck that Percival was standing outside with his pipe when he spotted it."
Mr Turnbull, who lives in the village, said: "I saw right away that it was part of a medieval cross slab grave cover.
"It was probably in an early church or chapel from which stone was taken to build this place. The carved design on it is of leaves. I believe this is the only medieval object in Mickleton, so the find is important.
"But I would never have been standing there and looking in through the door but for the smoking ban."
The building was a blacksmith's shop for many years before being converted into a workingmen's club in the late Fifties, and later it became a pub.
Efforts are now being made to trace any documents showing where stone was taken from and when it was put into the building.
Mr Turnbull, who runs an archaeology practice in Barnard Castle, emailed a photograph of the stone to Peter Ryder, of Northumberland, a national expert on ancient grave covers, who confirmed the identification.
Mr Turnbull said the stone should be left in the wall because it might be damaged if an attempt was made to remove it.