Michael Harkin, from Ederowen Park in the Galliagh area, still insists that he saw something strange hovering overhead while driving through Prehen last Tuesday.

"I'm not a big believer in flying saucers, but I suddenly saw it out the window as we came over the hill and screamed to Catriona, who was driving, to stop the car. We slowed down and were literally crawling along the road at about 20 miles per hour when I took the photo and by the time I had taken the photo and the car had stopped, it was gone.

"We must have only seen it for about ten seconds at the most before it disappeared, so we were actually really lucky to get that one photograph."

Websites and UFO forums all over the world have since picked up on Derry's UFO, and Michael says he will be replying to every response with details and co-ordinates of the exact spot.

On whether the photograph could be an elaborate hoax, 32-year-old Michael says: "To begin with, I wondered if it was some sort of helium balloon, but it was far too big. It definitely wasn't the tax disc on Catriona's car either, as that is still there, further down near the bottom of the window. Even though we saw it, I suppose it could have been a model space ship or something similar but it was just so big. It was definitely outside the car and way above us - I just knew it wasn't normal and that's why we stopped the car."

Michael says he and the car's driver, Catriona Horner, have been overwhelmed at the interest the photograph has generated.

"We're amazed that so many people seem interested in it. We only sent it into the 'Journal' because it was so unusual. Catriona has been defending what we saw too, she wants people to know that it's definitely not Photoshopped and the actual photo saved on my mobile phone is no different to the one I sent to the paper."

So does Michael believe that the truth really is 'out there'?

"I'm still a sceptic I suppose, but it was just so massive I don't know what to think."