Several times off the Irish coast. They sometimes get caught up in the Gulf Stream and end up on this side of the pond. If they are lucky they are taken in by some marine folks that ship them back to S.America but I have seen one or two caught up in discarded fishing longlines and they had to be put down.
... in Portmadoc Bay during the very hot summer of 1976. The local paper was full of the 'Barmouth Bay sea monster' after some children reported seeing it. The Natural History Museum, told me that there were about 50 reported sightings of leatherback turtles a year in British Waters at that time. I understand the incidence has increased since, but whether there are more around, or simply more people taking the trouble to report sightings, is not known.
I see from the text that some are thought to be wind-blown! Now, own up, those of you who have seen one or two. You recognised them by their rig, didn't you? So what is the modern leatherback turtle using as a sailplan these days?