We did a search in google along the lines of "black triangle doncaster 1997 -1998" and got a couple of interesting hits!.
Seems to have been a wave of sighting during 97 and 98. Here is a couple of expamples.
TWO MEN CLAIM A BLACK TRIANGLE UFO CRASHED NEAR SHEFFIELD
On March 24, 1997, at 10:06 p.m., a mysterious explosion rocked South Yorkshire. The boom, confirmed by Edinburgh University, was attributed to a
sonic boom from an RAF jet flying too low at supersonic speed or to a bolide or exploding meteor.
Now two men, one a ufologist who wishes to remain anonymous, claim they saw a black triangular UFO pass over their house near Sheffield and
Dronenfield, Yorks. just prior to the blast.
The ufologist's friend claims he looked out the window at 9:45 p.m. on March 24 and saw a large object fly over the house. He described it as a
triangle, "200 feet in size, with a light at each tip and a large blue intense light in the center bottom."
He also claims to have seen the object followed by six RAF Tornado jet fighters, "first two, then two more, then two more. Following that,
helicopters began to appear."
Hearing the explosion, the friend told the ufologist, and together they drove down Highway A57, also known as Snake Pass Road, hoping to find the
crash site. They then ran into a police roadblock, which prevented them from entering "the barrens" beyond Sheffield.
Rumors of a "Black Triangle" (BT) crash persist in Britain, despite the official denials. Supporters of the theory cite an alert that evening at the
Royal Hospital at Halamshire to expect the arrival of "plane crash victims." Also, there are unconfirmed reports of UFO radar contact at the bases
RAF Cosford and RAF Shawcross. Investigation of these reports by Britain's UFO community continues. (Thanks to Errol Bruce-Knapp for forwarding this
source : www.ufoinfo.com...
Black Triangle seen in Doncaster - 28 July, 1998 at 01.30
Early one summer morning, Stainforth mum Debbie Scorer walked out of her house to find a giant triangle hovering above her. To this day she does not
know what the object was, but it is the first of three weird sightings Debbie has discussed with UFO 2000. Debbie, of Fifth Square, Stainforth,
Doncaster, went out into her garden after thinking she had heard the sound of a helicopter. When she went outside she saw the huge shape above her
home with moving lights along the sides. The whole thing was slowly moving just above the rooftops.
The second experience was with her whole family as they drove through Stainforth where she, boyfriend Tony Curran and children Jamie and Thomas saw a
light in the sky. They described it as a big orange with the appearance of light and darker segment shapes. They first sighted it over houses and
followed it until they reached the end of Stainforth' s Kingsway, where it moved off towards Dunscroft Broadway.