In his book “Wings On My Sleeve,” Eric “Winkle” Brown of the Royal Navy, described a flying saucer sighting he made in February 1956, seen by multiple witnesses in SW Wales, UK

Source: https://archive.org/details/wingsonmysleeve0000brow

Here's the quote from Eric Brown's "Wings on My Sleeve"

"As Commander (Air) I was rather ruefully resigned to a full programme running the day-to-day air business of the station, with no excitement in the air.  I had just two exceptions to liven up my time while I was at Brawdy.
 
"The first was in February 1956, when one evening just as the last aircraft were returning to the airfield we had a phone call from a lady schoolteacher near Fishguard to say that she could see a flying saucer. My scepticism almost made me laugh outright as I listened to her, but I promised that I would ask one of the returning aircraft to have a look.
 
"Jokingly, we told one of our pilots over the radio what had been reported.  To our surprise, he said, 'Yes and I can damn' well see it, too'.
 
Again I was anything but convinced, especially as it was rapidly moving out of his sight.  Minutes later one of our air traffic controllers called down to my office to say that he could see it with the naked eye from the control-tower roof.  I shot upstairs and saw what did look like a saucer in the air.
 
"I decided it was interesting enough to go and have a look at it, and I leapt off in a (deHavilland) Vampire to see what I could make of it. I climbed to about 40,000 feet but the shape was still above me and moving fairly fast, and in the now half-light of dusk I could not identify it. But I am certain it was not a cosmic research balloon, which was the only tangible thing I thought it might be.
 
"The shape continued to be identified along the entire Bristol Channel coast that evening without any explanation ever coming out.  Where once I scoffed — I now have an open mind."